If it doesn't wind up ending over a natural hard point like a structural member...it needs the same coefficient of expansion (same material of the hull...often to the dismay of epoxy only types) and similar flex.
If interior members are providing the hard point to a degree and the patch isn't huge....then it doesn't need to mimic the rest of the hull as much.
I'm sure a specialist can explain it better...but that is my take on the research I have done.
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