The party size issues are interesting. Here's another scheme to analyze.
- Allow hireling dismissal (50% what you last hireling cost). Allows partial forgiveness for overspending, as well as fine control over scrap to equip more upgrades.
- Divide XP gains by total party size. Rescale XP per map accordingly. (This is similar to the advice to play at 300% XP on Hero Mode) This is different from requiring them to be summoned- you get stuck with the tradeoff unless you decide to dismiss units.
For (2), XP per unit killed would now be multiplied by a baseline expected party size for that map. This would not amount to a flat 300% hero mode bonus, though, and it could affect the mode's grinding curve dramatically. Since extra units cost scrap and psi, having them also cost XP could be a serious burden. On the other hand, if you maintain expected party size, the difference is zero.
The math for this proposal could get hairy. Does power scale with XP differently depending on how many units that XP is divided among? If so, is there one right way to do it that shortchanges the player of freedom?
This could be a separate option. "Adjust XP by party size" . The game already provides incentive for staying lean, but why not test it? Also, (1) by itself isn't too bad.