Judging by the dark spots on the sides of the bow, Id say plenty of heat is getting around to the back. You really need to prevent that. HHB is very sensitive to that, I found out firsthand. Seems if the back gets a bit over-dry just once, its tension strength is gone quite often regardless of how long you let it acclimate afterwards. If you are using a backed caul, don't, they reflect and capture a lot of heat.