I don't think low poundage causes tuning trouble. I am shooting .400 spine arrows with a 100grain tip at 53#'s and they are shooting just fine, well, as fine as I can shoot them . You can tune your bow to shoot the arrows just fine at 50#'s or 58#'s. The best way is to tune for the right DW closest to centershot but you can still tune away from that. If anything, I would think changing the tip weight to 100 grains would have accomplished the same thing as changing the DW as far as tuning goes.

Perhaps just feeling better about your setup is helping you shoot better. I know there are days when I feel like everything is clicking, there is confidence in my setup, confidence in the tuning, etc.and I can shoot great and then there are days when I am wondering what happened.