Traditional scopes can have their height changed by changing mounting rings.  But sights with a fixed base, such as the reflex sights suggested, don’t easily allow for this. 

 

Some smaller sights can be adapted to sit higher with a riser but some fixed based sights are just too long to work with a riser.

 

Ideally you want the sight to sit as low as possible and still be useable.  Too high and you can’t get a good cheek weld.  Too low and you can’t squish your face low enough to look through it.

 

The proper height can be determined by comparing the comb( top of the stock) to the top of the mounting plane.

What do you plan to mount this optic on?

A shotgun with a comb height lower than the scope mounting area

A shotgun with a comb height in line with the mounting area

A a rifle with a comb height lower than the scope mounting area

A a rifle with a comb height slightly lower than the scope mounting area

A a rifle with a comb height in line with the mounting area