The spagna manual states 28-31" above the stove top.

How big is your stainless back splash, and where did you source it from?

Range hoods have to be functional, and what contributes to that are:
- how powerful your range is and how you cook, so simmering is one thing, searing steaks produces a lot more that needs to be taken out
- how powerful the fan is
- how big the collection area is of the hood - where rising smoke/steam can be caught before the fan pulls it out. This is based on depth (top to bottom) and width and depth - if the hood is not over your front burners, then you'll have a problem. Your hood doesn't have much in the way of a collection area.
- how close the hood is to the cooktop, the closer it is the better it will work

Based on my experience, I'd strongly suggest installing the hood without the backsplash so that you can adjust the distance from the cooktop based on trying it out. We ended up dropping ours an inch and a half from the first place we put it. Once you're happy, do a more permanent install.