Shank my brother, when you gain weight whilst seriously training, you gain more muscles than you would fat. Now where do you think the 5kg or 10kg of added bodyweight is going to go if not spread all over your body.
And let me put your mind at ease even some more because I've got some suspicion that you still doubt what I'm sharing with you my friend.
When you did or will do your bench press and your b/neck press, would your triceps be assisting your larger (main) muscles with the lift or would the triceps be just a piece of meat sitting there doing nothing? We both know the answer but I'm still not satisfied and would like to give you more proof that your triceps is working overtime here, much more than you have ever though.
Proof:
Have you heard of the pre-exhaust principle? It's where you isolate your main working muscles from your assistant muscle/s. We have both agreed from my previous explanation that the tris are not merely sitting pretty whilst you're busting your ass pushing that bar off your chest or above your head; you're with me so far? Good...
Now if we want the triceps to go to sleep or rather take a nap instead, whist we're (say) performing our bench or press above head, we bring in the pre-exhaust principle and begin to do flys for the chest and side laterals for the deltoids before performing the main compound exercise.
Can you see what is happening here Shank? Flys= no tris, and side laterals= no tris. Now momentarily our chest and delts are fried whilst our tris are happy taking their nap. Now we move onto the main compound exercise and we find something beautiful has just taken place. We find that every rep in our compound exercise is actually felt by the muscles we've intended to train, i.e. chest and shoulders. Why do we feel that way? Because these muscles have been previously fried (pre-exhausted) and now find that they would have to do all the work where the tris are still waking up from their earlier nap feeling fresh and strong. Why? Because we have eliminated them (the tris) from getting involved earlier and now they are still not going t play a big part in our compounds because our main muscles are going to give up way before our fresh tris (which are usually the bottleneck/weak link) in these compound movements.
You Shank, are not performing pre-exhaust anything which means your tris are going to fry and that my friend = SIZE!
PS: Don't forget, that just because you don't feel sore in your tris after the bench or the above head press does not mean your tris are not receiving a good stimulus.
Fadi.