I do “bids” based on the relative difference between sides. If I am much better, the Allies could get up to 100 PU of extra units. If they are much better, I usually just give an extra UK sub in the Med. In games of even skill, the bid is typically in the 20-40 range. We definitely see from League games that the Axis can still win >50% of the time even with a 20-30 PU Allied bid. I think that approximately 40 is now necessary to give the Allies a 50-50 shot of beating a skilled opponent.
Just mention the word bid and you will start to hear people whining that the game MUST be balanced because it MUST, and how they are able to beat lower-skilled opponents without a bid, or some other long rant. Yawn…