One thing I have noticed in my latest playtest is that the fact that you can produce units might lead to more offensive behaviors since your units can be easily replaced.
Also reinformcement has the problem of placing units on the back, requiring extra movement to put them in combat range.
It somehow reminded me of chess, in that game, you generally move cautiously, and position your self before attacking. If you just send 1 or 2 pieces in offense, you might easily get trapped.
So I want to create the same feeling with my war game. One possible solution is to remove anyform of reinforcement, or strongly limit the number of reinforcement or the occurence of reinforcements. Could be only useful when stating to lose the game and when the ennemy is at your door, else it would require much more movement to bring those units from the reinforcement point to the battle field.
Another solution is to increase ties between units forcing them to work together. So that sending 1 unit alone will have little chance to survive. I can do this with interceptions, spotting/scouting mechanism, etc.
Else without reinforcement, there could be a problem where the game cannot possibly end, or a player cannot win, because certain type of units are missing.
It's again for the same modern game.
Reinforcement could come out of a building, like aircraft from airports and land units from base.
The way I am thinking for reinforcement is that each turn your reinforcement track increases with time and some outcome of the game.
Player can decide to wait to get more forces, but less often, or ask for less units more often.
It's also possible, that you can 1 reinforcement per game, giving you a dilema on when should you reinforce.