I don't have the book in front of me, but I don't remember seeing "SEPI"; assuming you mean just PIs, then mostly you've got it, except:
- don't forget that the 90 minutes also includes warmup and cooldown
- PIs are supposed to be at least 100% of HR/101% of power from the field test. for power, I believe the book recommends shooting for 110%-130%. if you can't keep above 101%, you're burnt out, don't do any more intervals.