Hi,
My DD1 needed to reduce her A times when she became more mobile too - for her it was just a lot of work and she got tired quicker. So, I think it can definately be the case for some kids! It sounds like you are really cued into your child, so I say follow your instincts, things seem to be going well for you. I know it would be nice to just make that transition to one nap when you'd like it to happen, but it can take SO long to work itself out! In our case, it was a good 3-4 months. I know some kids can do it quicker, but it wasn't that way at our house. Anyway, I say go with what is working!
katemom