Hmm..I'd guess it was OT at BT but tbh I'm not really experienced in routines with those short naps in the morning as mine had to have a very long morning A time to have a nap.
That afternoon nap was shorter than the other EASYs you posted though.
Hmm..he was getting significantly more sleep a month ago with the longer morning nap and long over night sleep.
Here's a totally different idea - what if the first nap was longer at nursery, maybe 11-12 and then you didn't give a second nap until after the school run? Don't know what time you are back from school PU but maybe something like nap at 3.15/30 - 4.15/30 (would he nap 3hrs after first nap?) and a 3.5hr A time before BT so 7.30/8pm BT??
Most people are reluctant to move BT later, I know I was, that Y time in the evening is precious but we got used to it really quickly when DS's BT moved to 8pm. It shifts the overnight sleep to make a slightly later Wu easier (I'd think 6 to 7am rather than 5 to 6) and then helps both naps come later in the day so that you can fit that school run into A time?? Something like two one hr naps and 10-11 hours over night.
It might also give some tweaking space so that the morning nap can move to 11.30-12.30 for a short period and then make the leap to an at home nap at 12.30 which is a hard jump moving 1hr in one go but not impossible especially if he gets to the point of morning nap refusal.
It's just an idea, or another idea, to throw into the mix.