I'm going to suggest you pick a suitable WU time that fits with ~11hr night and a BT you're happy with (some compromise may be required). Once you do that, you pull WU later by saying that first nap will be after 3:45hr or 9:45, whichever is later. 3-4 day to a week later, you would shift that to being 3:45 from WU or 10am whichever is later until WU is at a reasonable time.
I agree that its not a good idea to cap the first nap at the moment.
If he's super tired for his morning nap and sleeping 1:25 (a slightly UT nap), it may be worth considering a change of activity rather than nap as he may just be a bit bored or going to sleep after 3:30 from habit.