I haven't ever really bothered to measure so can't give you exacty numbers, but with Escudo's coin shaped disc like flakes I find that I prefer slightly shallower and skinnier conical bowls such that one or perhaps two coins, folded once and stuck in vertically (side by side if two coins) fill up the bowl, with perhaps a small bit sticking out of the rim to press down and snug up the pack. My Yakslon Rhodesian is such a pipe as is my Stanwell 191, one Escudo coin fills up the Yakslon with a perfect pack. For typical rectanglarish flakes (Orlik Golden sliced for example) I like a deeper bowl (but still not super wide) such that a flake or two folded once horizontally and once vertically will slide down into the bowl completely and provide a slightly looser pack than I use with the Escudo coins. I had a Luciano Cherrywood that had this sort of bowl and made for a good flake smoker, although I traded it away. A Stanwell 63 and 30 also seem to me to fit the bill for these sort of flakes.