I have noticed that when I want to add troops to an army with more than 2.0 of experience I actually end up with less hitpoints.

This doesn't seem to be an issue when I add a lot of troops, but if I add like 200 troops to an army of 20,000 soldiers the problem appears

adding untrained troops to a trained force will always lower the HP. Think of it this way, if 200 noobs join an army the vets will need to look after them a bit so they don't do anything stupid hence reducing their effectiveness by a bit.

When you add new troops to already trained ones, the total EXP is spread over the new number. If it goes down a lot, you end up with less than you startet with.

AFAIR the devs are still tweaking that one? If it is that hard for 200 in 20k, it definitely needs some ;lame

EDIT: meh, too slow I was ...