That sounds about right and this kinda validates your math.
https://www.omnicalculator.com/construction/snow-load
So according to this you exceed the maximum snow load for a flat roof in NY and need to shave an inch off the top based on a “settled snow” load. I lived in NH for 20 years and we raked the roof when we had 10 inches or more if we were expecting back to back storms.
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