What's the mission?

[Imp]

No way to know once starts as far as I know but think allotment varies along thes lines.
Assume meeting so should be same sized force for simplicity.
Player 2s Support is sum of player 1s Core & support minus player 2s Core.
Example
Player 1 core 2750 buys 250 support for 3000 total.
Player 2 will now recieve support to take his force to 3000 points to
It probably tailors slightly like if player 2s core is already 3000 still recieves a few support. Also the reverse if player 2 only has 1000 left in core he will not recieve 2000 support game probably looks at player 1s support & adjusts something as simple as cant be more than 4x the other players would restrict but probably a bit mor complex.

The upshot is hopefully side with smallest core should get more support points so one might get 300 the other 700.

First battle when both sides cores are near enough identical both sides will get the same amount of support points, this can be controled by player 1. If he is offered 500 support points but only uses 50 player 2 will get 50 to if he spent the full 500 they will be offered that.

I think thats how it works.

A note on repair point dicrepancy there are several ways round it if want to be a gentleman & get the other player back in the game.
Easyist is have a light engagement. Adjust map size & just use one infantry company or whatever you agree on, sort of advance scouting with part of your core only. gives a change of pace & get another lot of repair points to get him back up to strength.