Cyndie - I think if he naps more than 2.5hrs in the day now you are probably going to get a shorter night. I find the same, in order to get a decent night from O on a 2 nap day he needs 2.25hrs max. On a 1 nap day he can probably sleep a touch more in the day & still give a good night.
There are also lots of babies who still do shorter A times at your LO's age - he's 13-14 months now right

My friend's LO is 15 months, he wakes at 7am & still naps at 9.30am for about 30mins & then again at 2.30 for 1-1.5hrs, BT at 7pm. She's never done BW but has just stuck with the same nap times for months & he wakes up when he is ready, she never ever has to wake him. As he has gotten older he still goes to sleep at naptime no problem but his naps have just shortened naturally, as he started to need more A. It just goes to show that short AM A times can work for some!
I think if J is starting to wake earlier again he is trying to tell you he needs more A somewhere. Since your PM nap is limited to a set time by school runs, I'd be inclined to perhaps cut that AM nap down to 15/20mins. You might also need to push it a touch later, so it is from say 10-10.15am (obviously do this gradually though) as if you did 9.45-10am he might struggle to last all the way to 1pm.
What's the latest he can sleep until before you would have to wake him to collect DD from preschool? If he can sleep until 3pm the other option would be to gradually shift that AM nap later so it runs from 10-10.30 & then shoot for a 1.30-3pm nap. That way you restrict his day sleep to 2hrs meaning he isn't getting too much, it gives him a good 4hr A time to BT after that PM nap & should also hopefully encourage him to wake later b/c his AM nap is later. How about that

Sabs - thanks. Alyssa does sound like a tricky one! We too get longer nights if he short naps during the day - I guess they have to make up for it somewhere. Try not to worry too much about the 6hr A. We had 8hrs the other day & he slept OK overnight & we got back on track within a day.
lulunut - we sorted the EW by pushing out the AM nap. It was brutal, but basically I had to stop letting him nap before 9.30am at the earliest. He got very very tired & miserable for a few weeks & I had to avoid going in the pushchair or car around 8/9am in the morning for a while 9as he would just fall asleep) but it has really worked. I also kept the AM nap short to stop him using it as an extension of night sleep, & then allowed a longer PM nap.
Ladies - we did another 2 nap day today.
Wake: 6.30-6.50am (not exactly sure when. So 11h 40-12h sleep - but only due to rubbish naps yesterday)
Nap: 10.00 - 10.30 (STS in 2 mins flat - he was shattered)
Nap: 2.00 - 3.30 (he woke at 40mins & 1h 15 but resettled. Think slightly OT. I woke him from nap.)
BT: 7.00
I'm quite pleased with how today went & hope he does a good night tonight. Still a little concerned 3.5hrs A isn't enough at the end of the day though.