Not a 60-70% deficit; 60-70% of maintenance. It's cutting out a math step. Instead of, say, 0.3 x 1500 = 450; 1500-450 = 1050, it's 0.7 x 1500 = 1050.
But I have to admit, Etana and Espi, aside from that my math skills are flummoxed. I seem to recall a while back that someone asked Leigh how frequently one should recalculate maintenance calories while on OPT, and I
think Leigh said it's not necessary to recalculate until the end of OPT. Like Espi said, the .4 deficit of the initially calculated cals should take care of the decreased activity.
I think that was somewhere on this board; I may be able to try to search for it later, but I have no clue how I happened upon it in the first place.