As noted in a very recent article, I have several horns I can and do use regularly. One common adjustment made on horns is to add “dimes” to the valve levers, to meet your fingers better (more here).
But you also have a thumb. Going back to the triple again for a recording project I noted the thumb valve is really not quite the right place for my best technique. Some horns have adjustments built in, but triples often not so much, the space is really tight with the two thumb valves and in my case two thumb valves and an extra button for the stop valve.
In this case, when I first purchased this Paxman model 83 I hit upon gluing a piece of plastic tubing on the F/Bb change valve to position it bit better. I played the horn full time for several years that way, then went back to a double as my main instrument, I was no longer often playing first horn. In that time frame I took the tube off and switched the horn stand in Bb, which I think was how the fine folks at Paxman thought most people would set the instrument up. In Bb I think the thumb valve position as delivered is quite good.
I set the horn to stand in Bb for some time for use in solo and chamber music, but I need it to stand in F for “real” horn playing, my brain stands in F! Coming back to it from double and needing to hit full technique on a variety of music I added the tubing back again as seen in the photo.
The tubing is available at anywhere that sells hardware. I cut the section of tube needed to cover the lever with a sharp hobby knife. As a model railroader my glue of choice is Walthers Goo, available at any good hobby shop that stocks model trains. It is a great contact cement that I have used to fix many mutes as well. Follow the instructions on the tube; I also clamped it on the valve for several hours as you don’t want the tube falling off! Most of the other valves on this horn are string action and have a bit more adjustment built in — but the F/Bb change valve is mechanical.
This general technique of gluing on a piece of tubing is an easy fix toward getting a problem valve in the right position and also completely reversible if you wish to remove the tube later. Alternately, you can affix something else. I have on a prior instrument added a layer of cork to a thumb valve and a student I had at one time had mounted a block of wood on a thumb valve paddle to build it up.
The overall point being you have some options, there is no need to suffer along with feeling you can’t quite reach a valve optimally.