Imbracablecrunk , the CFM 56 flat rating is ISA + 15 c = 30 c . I have fed assumed lesser than that ample number of times . Try it out when conditions permit , or may be assume an example just to check it out ..
Hmmm. Maybe you can't reduce unless the assumed is at least a certain amount more than actual. I know a few times I've tried, and it simply wouldn't accept the assumed temp.