Engine timing the same, displacement the same , a longer stroke will place more leverage on the crank that is how it makes more torque. A bigger bore makes more rpm because the dwell at the top of the power stroke. They both have to do with the angular movement of the rod to the crank stroke. As you increase one you diminish the other and vice versa.

The true problem is we deal with small displacement engines; if you increase the stroke .007in, who cares if it makes .003 in oz more of torque.

Changing the characteristic of the engine with rod length, port timing, combustion chamber is how you broaden the power usability once you settle on your bore/stroke.