I wouldn't conclude anything after just one day/one night, yk? I would do like you, keep the nap at like 6h after WU, let him sleep max 2h and keep BT as usual. But I would give it a few days before we can assume things. Like I said before, an 11h night is still a great night and not short at all. I know it's not his usual, and sure, you can try and help get things back on track with shifting the nap, but it might just be that he grew older and needs less sleep at night.