Do you think he is maybe in a UT/OT loop? Maybe the fact that you put him to bed so early is causing to wake early which then makes his A to Nap time really long and makes him OT. I know his LSN, that's why I wonder....
I am finally realizing that with Liam he needs a 12.5hr day after a good long nap. I can't get more than 11.5hrs of night sleep out of him with a long nap. Before, I was so scared of him getting OT that I made BT too early (11-11.5hr day), got a short night 10-11 hrs, or put him to bed too late (13hr day) and got 10.5-11 hrs. Generally Liam won't fall asleep of he isn't tired, but I am finding that he does fall asleep because he is so exhausted by the move to one nap and shorter nights and then the cycle never ends...
Maybe once yet get a better WU time and a decent nap you can try BT a bit later.?
The problem for us is that the naps aren't that consistent and I haven't figured out the right time to put him down after a shorter nap and then we get an earlier wake up which messes everything up once again..