I am remodeling my kitchen and my contractor is installing a stainless venta hood 36 inches and my new professional range in stainless is 30 inches- is that a problem that they are different in size? It seems odd to me.... HELP!

Its a great idea. The small margin at each side helps capture contaminants even without turning the unit on. Very smart.

Sounds like you have a knowledgeable contractor who knows a bit about ventalation. It's a plus