Why do some buses have noses and some are flat in front??

I'm interested in a bus in this model/style. Flat nose/front engine with 10 windows (28 1/2' long). This one specifically is an International AmTran FE. I've also seen the Bluebird All American

Why do some buses have noses and some are flat in front??

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Why do some buses have noses and some are flat in front??

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