Hey Joe,
I'm not sure about the size of the bowl actually making a difference where heat is concerned. But, there are definite differences when smoking different types of blends.
This isn't a hard and fast rule, but more my preferences. I'm not talking about wall thickness or grain orientation that's a different issue when talking about heat.
Large Bowl pipes: Aromatics, e.g. Lane 1Q, BCA, Cavendish, Maple or Vanilla flavored tobaccos.
Small Bowl: English blends, VaPers, (this is probably where some differing opinions will come in) Flakes e.g. Escudo Navy De Luxe, or PS Luxury Bulls Eye type of tobaccos.
That's my two coppers.