If my chunk is just a little too big, I split a piece off using a hammer and a dull chisel. I usually use 2 or 3 pieces of varying sizes per smoke anyway. Smaller piece gives off more smoke in the beginning, larger piece for sustained smoke. I don't like it if my lid doesn't close, but I also doubt if that is the cause of your different smoke tastes. I'm not sure of the source of your oak, but even if it comes from the same tree, different parts of the tree can be more or less dense than others, and will dry and burn differently.