If this helps at all, I just realised yesterday that after merging A & set times, Jr has kinda regulated himself. We have kind of settled into set times now. Perhaps he is old enough for it now. The only time the routine goes wonky is when we keep him up too late/overstimulated at night because we went out for dinner/party, and he early wakes. This can happen quite a bit, in fact we have a dinner party tomorrow. He takes a few days to recover (earlier nap and EBT) and is then back on track.
Now he does,
WU: 0800 - 0815
Nap: 1415 (+/-15 mins), He naps for 1.5hr - 2hr15, I don't wake him up. Can be between 2.5-3hr if he is catching up from OT
BT: 2100 - 2130, Depends on what time he wakes from his nap. He is usually put down for bed between 2045 - 2115.
I noticed that he does best with 6hr - 6hr15min AM A time and 5hr - 5hr10min PM A time, with a 2 hour nap. He can handle a 13hr15min day without getting OT.
Oh, and he was indeed OT last week. I pulled back his morning A time back to 6hr-ish and EBTs and he caught up in 2 days, and self regulated to the above routine. Of course, there are days when he is cranky and refuses sleep, and there are days where he would just sleep. So, I just decided to go with the flow. On difficult days, I just take him to the jungle gym or swimming pool...