Ali, I know the first A time seems incredibly long but at 5.5 and 6 months this was the only way to get my DS to sleep a full first nap, which is why it doesn't seem all that strange to me. Once mine was sleeping a good first nap again (after the 4 month regression we had at 3.5 months - 5.5 months) I was able to reduce the A a bit and keep the first nap long. The following A times were much shorter.
Looks like he's falling to sleep independently and able to transition alone so long as he doesn't have a dirty nappy or is hungry...
After looking at the times you've given I wonder if you might try something a bit different. Usually at this age we go by A times and don't look at set times until LO is around 12 months, but some LOs respond really well to set nap times and I wonder if yours is one of them. It appears that he is looking for food almost at set times regardless of when he had a top up or solids, would you agree? And the first nap seems to work relatively ok at around 9.30, on Friday when you tried a 4hr A time this took his nap to 10am which he wasn't happy about, but Wednesday he did great with the 4hr A time BUT nap came at 9.30.
Looking through the EASY times with a more 'set' routine in mind it looks like he may be happier to set all meal times and work naps around them. It's almost as though his body clock is guided by those meals times (eg 10 - 10.30 nap wanting E at 11??).
If milk feeds are 'set' to 7, 11, 3 and 7 (which is a regular routine with some give and take) perhaps you can fit in one decent nap in the morning, continue to try a W2S for nap 2 and reintroduce a third nap (CN) as Ali suggested to cover some time before BT.
I'm not suggesting this as a long term solution but more as an experiment to see if he would be happier and more predictable if you followed his E times rather than A times.
The day might look something like this:
WU - any time 5.30 - 6.30 ish
E 6.30/7.00 (the earlier time if he really needs it)
E solids 8 with water and/or top up milk
(A roughly 3 - 4hr)
S set time 9.30 (as long as he will sleep)
E 11
E solids 12 with water and/or top up milk
S 1.30 - 2.30 (or longer if he will)
E 3.00
E solids 4 with water
S 5.00 - 5.30 (if CN is refused EBT)
E 7.00 (if CN refused 5.30)
BT 7.30 (or EBT 6.00)
[I've put in 3 solids meals times for guidance, he doesn't have to have 3 solids meals at this age but looks like that's in your routine anyway]
The possible danger I see is in that first nap could go short if he is not tired enough and morning WU could move earlier than you'd like if he tries to regulate that first A time (ie waking at 5.30 instead of 6 or later) but we would be able to see that happening and take action if/when needed.
If the second nap is longer or if the second CN is refused you could go for EBT.
What do you think?