Ok, so average A time for 6 months is 2:45 to 3hr, so 2.5hr would be the low end of reasonable for his age, I'd think. Give it a few days with 2.5hr as your A time, then increase again if you're still getting short naps.
We've had a terrible few days, early wakings of 5am. Short 40 min naps, I feel like we've gone backwards
These are all symptoms of insufficient A time.
With the short nap, you may have to try to resettle for the first few days while he gets used to it again - try sneaking in around 35min into the nap and just watch for him to stir and shush/pat or whatever method you use to settle him and see if you can get him through the transition. If he still wakes, then its best to shorten the next A time a little, maybe by 20 min and see how he goes then.
When the routine is all over the place, it can be hard but just to keep things in the EAS pattern, I'd probably do solids an hour after milk and do milk when he wakes, even if its a bit early. Just my 2c though, others would keep the feeds further apart by waiting for a while after he wakes if he takes a short nap.