You are correct on home construction. It is surprising however that in large commercial some of the best fee limitation and cost savings is for “Cost-plus-a-fee with a Guaranteed Maximum Price. In 47 years and running hundreds of millions in projects, I made some of my biggest profits on lump sum contracts.
Same boat here. I ran a family custom home (and spec) biz for a decade a d we made the most money on fixed priced contracts. There’s a premium for predictability and typically had a dozen or so homes going at once and were able to get economies on contacts with subs and fix those prices, etc. You know how more works.