That's actually pretty normal, especially for tall people. Tow solutions:

1. Don't use the waist belt. A simple webbing belt doesn't provide any support anyway. Cut it off.

2. Pay a lot more money for a 2200 cubic inch day pack from a company that does make them in different sizes. Osprey, Gregory come to mind.

Note however, that this sort of pack might not work well sitting on a snowmobile.
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--Ken B