Silicone recommendations ( for setting knots)

Here’s a pic of one I set the other day. You can see how the base of the knot is seated all the way down and flush with the bottom of the knot socket:

Yep I got you that's a good example. 
I guess there is a chance mine tapers to the bottom of the hole, because it is a pretty snug fit.

Here's the about the way this one was sitting and this is after it pulled up and back in there for a picture. Just down there a bit more than this and hiding that plug.
     It's funny I never noticed how rough that inexpensive AliExpress handle looks until I've magnified it it really looks bad, lol.  Just kind of a test handle anyway though.

Here's the about the way this one was sitting and this is after it pulled up and back in there for a picture. Just down there a bit more than this and hiding that plug.
     It's funny I never noticed how rough that inexpensive AliExpress handle looks until I've magnified it it really looks bad, lol.  Just kind of a test handle anyway though.

Ya, that knot seems like it should be set much lower or if you really want that much loft, get some spacers under it.

I use Grolsch beer bottle gaskets (which include a free beer) or thick nylon washers that you can buy at Lowe’s or Home Depot

Oh, and I was going to mention that knot diameter looks too big for that socket... what size knot is the knot and what size is the socket diameter?

Here's the about the way this one was sitting and this is after it pulled up and back in there for a picture. Just down there a bit more than this and hiding that plug.
     It's funny I never noticed how rough that inexpensive AliExpress handle looks until I've magnified it it really looks bad, lol.  Just kind of a test handle anyway though.

Ya, that knot seems like it should be set much lower or if you really want that much loft, get some spacers under it.

I use Grolsch beer bottle gaskets (which include a free beer) or thick nylon washers that you can buy at Lowe’s or Home Depot

Lol, pay for the gasket and get the beer free.
   I do have some of the plastic washers on hand, they worked out really nice on another handle.

There has been some great input and I have a couple of ideas. I don't set knots, though have made an awful lot of knives and straight razor scales. A dremel is a great tool if the knot isn't going all the way into the due the a tight fit from the handle. Based on what StubbleDaddy said, that may be much of the issue.
My experience is with marine two part epoxy and you are interested in Silicone, so this may not apply. That said, the marine epoxy is very sensitive to surface preparation. The one I use is one of the strongest bonds in the world, though if you epoxy two smooth surfaces it will ultimately come apart. It requires roughing up the surfaces with extremely course sand paper to give it something to hold onto.
The epoxy is also very sensitive to surface prep, which I do with Acetone and paper towels. The acetone will get rid of any oil, grease, etc... The manufacturer said to use paper towels as the slightest amount of fabric softener will keep it from bonding - that rags around the house may have traces.
I also think there is something to be said for using hot glue on knots. The knot will come out if you use really hot water during use, though it sure is easy to get them out if you want to change knots.

There has been some great input and I have a couple of ideas.  I don't set knots, though have made an awful lot of knives and straight razor scales.  A dremel is a great tool if the knot isn't going all the way into the due the a tight fit from the handle.  Based on what StubbleDaddy said, that may be much of the issue.
My experience is with marine two part epoxy and you are interested in Silicone, so this may not apply.  That said, the marine epoxy is very sensitive to surface preparation.  The one I use is one of the strongest bonds in the world, though if you epoxy two smooth surfaces it will ultimately come apart.  It requires roughing up the surfaces with extremely course sand paper to give it something to hold onto.
The epoxy is also very sensitive to surface prep, which I do with Acetone and paper towels. The acetone will get rid of any oil, grease, etc...  The manufacturer said to use paper towels as the slightest amount of fabric softener will keep it from bonding - that rags around the house may have traces. 
I also think there is something to be said for using hot glue on knots.  The knot will come out if you use really hot water during use, though it sure is easy to get them out if you want to change knots.

Dremel is a good tool. After some good measuring/ looking if I need to bore my handle hole a little bit should be easy enough with the ole Dremel
     That's good to know about the marine grade epoxy. Anytime I've used epoxy for any little fix repair or whatever it really bonds good. It's interesting what the manufacturer said about maybe rags laying around could have the trace of fabric softener and would prevent your bond, I might not have considered that.

I got home from two days on the job and did a bee line for my brush/handle.
   Ok what I've discovered was 2 things. The hole in the handle actually gets smaller toward the bottom I will try to add pictures of this.

So I was only getting the plug in the hole maybe halfway approximately of the 12 ish mm
Edit: Stubble Daddy was right, the plug wasn't going to the bottom of the hole.
 Depth

But I found the real culprit the glue bump in the brush is actually bigger than the plug on the bottom of the brush.
  I kind of found this out from boring the handle a little bit more with the Dremel still it wouldn't sink which is fine really for where I want to put it. 
    So I will silicone 2 plastic washers in the bottom to take up the space.
 With the Permatext 80050 in hand now, it should be all good and problem understood too.

I set two knots last year, both well over 12 months ago, using this; zero issues, fwiw:

https://www.amazon.com/gp/product/B0002B...UTF8&psc=1