It might just take a little experimenting.
I definitely agree with that! Each LO is different; there's no "set" formula. I know some babies like a good 40 minutes knocked off their following A time...my DS prefers ~15-20 minutes less. But even then, some days he wants that 40 minutes earlier. I'd just watch your LO's sleepy cues to see what he/she prefers.
Whenever LO has a short nap, don't worry so much about the exact time of day. Remember, EASY is a structured routine, not a schedule. That said, anything over 1.5h is a restorative nap. If your LO sleeps only 1.5h and there's 30 minutes before the next E, that's okay
If your LO sleeps up until the next E time (but not more than ~2h), then I would wake him/her up and do E. So, his day won't look like it would have if he hadn't had the short nap--maybe it will if your LO can do long naps--and as I said, it's completely fine. You're just adjusting his day to meet his needs, and to prevent OT.
Like pp said, we can see if your routine gives any insight. HTH!