If you add a percentage of rice flour or cornstarch to any sort of breading or pancake, you get a much crispier crust than one made with 100% wheat flour. The Vietnamese banh xeo, which is like a crepe made with just rice flour and coconut milk, no egg, comes out extremely crispy, for example. What is the physical reason that these pure starches cook up crispy?
My guess would be a lack of gluten in those flours. Gluten makes dough sticky and dense, so adding flours with little to no gluten might make it less sticky and thus crispier.