So give loyalists a steady C-bill boost per FP match, win or lose, the same across all factions. You can start with a baseline and adjust up and down depending on win/loss, or just go with a constant sum. This represents their access to rearm and repair, logistics, supply lines, etc.
Mercs receive a winning performance boost (modifed as it is now by %population), but make it higher than the highest a loyalist can make on a victory. This represents bonuses, combat salvage, and negotiation.
So you end up with this:
- On a loss, the loyalist makes some extra C-bills, the merc none. Hypothetical: 150,000 C-bills vs 0 C-bills.
- On a win, the loyalist makes some extra C-bills, the merc a lot more. Hypothetical: 250,000 C-bills vs 400,000 cbills.