I tried understanding this part but this is making no sense to me. The 146% you mentioned earlier came from the 1.46x the speed multiplier (13 vs 19). Not from 2.46x. Otherwise it would be 13 spells vs 32 spells in triplicity xD Which would def be more then 98.4k dps.
So you are not casting 146% faster but:
(19-13)/13 = 46% faster. Which would mean your 40k should have been a bit less then 60k dps with that faster speed. But for some reason you reach past 60k. Which is partly because of better rotation and the other part is the exponential triplicity dps effect. Which will now be removed/equalized with this deminishing return.