Hi there, agree with Laura. If he's not doing a long nap then he will get OT with a day that is too long. Activity increases but they need the sleep for stamina. So if they don't do a long night and don't do a long nap then their sleep totals fall below average in a 24 hour period and for most that means an OT kid.
Our long story short, Finn is 16 mths and we had EW until about 2 mths ago. Now we occasionally get them but not as often, and usually with a bit of tweaking we can get him to 6 a.m. Nothing later I'm afraid. The only thing that has really changed is all his teeth came in (just waiting on 2 yr molars). So I do believe there is some truth to the teeth causing a lot of sleep havoc. He would be rested enough at that 10 hour mark to be annoyed by the pain and just not go back to sleep. Now we know that he's actually capable of doing 11 hrs. But it took us nearly 16 mths to get to this point. He's just an early riser period, nothing we do can change that I think. So we have to build the best routine that will work for him, even if it doesn't work that well for us :-(
I think if you follow what Laura has posted, then we can start to push his day back. We ended up at a 7:30 bedtime for a while which gave us a 6 a.m. wake up. Now we got some bedtime resistance in the past 2 weeks so we have had to cut our nap to maintain bedtime. Now that his nap is slightly cut he's ready to do a longer night. But every LO is different. Seems your LO prefers his night sleep to his nap so you need to give him a longer night in bed if you know he's not going to pull of a long nap.
One thing that may throw things of is if you put him back down again too soon after the EW, he is not inclined to extend his night sleep and also, he may see that as his a nap rather than part of his night sleep. So he is also not inclined to give a longer nap either.
I know it's hard, Finn is in daycare and we have little control there too. Our day was front-loaded so he would do a really long morning A 6-7 hrs some days and then a much shorter A to bedtime, sometimes we had to cut as far back as 4.5 hrs. Now he's doing well with a 6 hr morning A, 2 hr nap and then no more than 5.5 to bedtime.