A circle minimizes perimeter, and by extension, a cylinder will have minimal surface area. This lack of surface area will slow the conductance of heat and the penetration of moisture.
Pastas comes in various thicknesses too, so not all brands or sizes will have the same cook times you have listed above. In my cupboard I have 1 box of penne that lists 10-11 minutes, another that lists 6-8 minutes, a box of pastina that lists 4-6 minutes, and a box of spaghetti listing 8-9 minutes.
Also note that different pasta shapes may or may not be ideally fully cooked, as some are better served al dente, while others are not.
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