HOMM3 Ratings and Stats

N - the number of ranks (for creatures:) )
A - initial points (1500???)
Z - approximate maximum, which the top 1 player has; add a bit to it so that this top 1 player doesn't fall into the first rank (so there's something to strive for, within reasonable limits)

here's the formula for determining the point step

S = (Z-A)/N, if any value drops, you can redistribute it later

you can also manually adjust the ranges depending on the difficulty and ease of earning points in the upper/lower parts of the tables