[Nick_K]

AFAIK research points should be fixed for all units. The formula is something like:
Base value (2, I think) + sum of magic paths + experience + any special +/- the unit gets (e.g. sages & wizards get a bonus) + magic/drain scale effects + effects of magic items.

I don't think you should get less than 3 RP unless you have a drain scale or the unit has some innate penalty. RP do vary between units of the same type if one has more random picks or experience.