9 month old: chronically overtired? Help!

[Tiramisu]

I would like some input on how to help our 9-month-old foster son get better sleep, especially daytime naps, and get out of what I suspect may be an overtired spiral.
A very good day looks a bit like this:
7am awake
Breakfast
9am bottle
9.15am  nap
10.15am wakes
11.30am bottle
12am lunch
1am nap
2.30am wakes
3pm dinner
6pm supper
6.30pm - 7pm bedtime with bottle
But that's not usual. It's hard to say what an 'average' day is, but generally he is more often tired than not and seems to just struggle though, he might follow a 45 mins morning nap with an hour afternoon nap, but he still doesn't look refreshed enough to make it past 5pm, 4pm is a struggle some days! If I miss the afternoon 'window' because of a need for a nappy change at the wrong time, he is very difficult to put down and can miss his nap completely.
I tried putting him to bed earlier, but then he wakes between 2am and 4am and can take up to an hour to settle again.
   
We had been following his previous routine (from bio family) of 6am-7am wake-up, 4.5 hrs awake time, 1st nap starting between 10.30am and 11.30am, 2nd nap at an unspecified time in the afternoon and 7pm-7.30pm bedtime for a couple of weeks, without huge problems. But a few weeks ago he started having shorter naps and looking tired most of the time.
He suddenly stopped napping long enough on this routine and was overtired and cranky. He had quite a lot going on when this started happening. He came off medication, started sitting, started on proper food, started learning to crawl... and got 3 teeth!
So I had been trying to learn his tired signs, with a 2-3hrs awake time for his age at the back of my mind... what am I doing wrong?

[Emami]

All those changes can definitely have an impact on sleep and his mood. Sounds like he has had a lot to deal with. Was he napping well with the 4.5hrs A time?  I think you were probably right to cut that back, but all the way down to 2hrs15 seems like too much I think. If he was handling 4hrs+ and you've cut it right down to half the A time he likely isn't tired enough to sleep a full nap. 1hr sleep isn't terrible but it's not enough to be fully rested either, so you are probably getting stuck in an UT/OT loop where he's not tired enough to sleep a full nap so then he's cranky and doesn't quite catch up the rest of the day. I would try pushing the first A back out to more like 3hrs and see if that helps. But he could just be adapting to everything that's going on and will settle down again.

[Tiramisu]

He had been sleeping well for 2 weeks, then all those changes I mentioned happened and he started showing tired signs very early (ie after 2 hours). Yesterday I put him down for his first nap a bit later, at 10am, but he only slept 30-40 mins. He then slept a short nap in his buggy at midday, but only managed 15 mins in the afternoon when I put him down in the afternoon, despite looking very tired. Perhaps I should keep trying the 10am and hope it works! I'd never considered putting him down later would work as he's already so tired at 9am.