If you are both happy, I wouldn't change anything. Maybe he really needs a long nap, and he's not ready to give it. We had a period of short nights and bt resistance at the same age of your ds and I was tempted to cap the nap (he was doing 2.5 h on average). But my ds did not sleep longer when nap was shorter these days, so I did not and after one month he took longer nights again and bt resistance finished, with the same nap lenght. So in my case it was developmental. It was only after 2yo that he started having longer nights with shorter naps, and then I Understood it was time for nap capping.
I must say that my ds always did 10.5-11 h nights.
Anyway, as a general rule, I would say: if something works don't fix it. It should not be exactly how it is in the book, you have to look your kid and see if he's happy, this is the most important thing.