Do you have the 20 MOA mount arranged with the high end in the back? Do you anticipate using a sunshade? Both of these will factor into ring height, along with the scope length and position in the rings.
The mount should slope down in front, so that the barrel has +20 MOA up angle when the scope is level. I don't mean to insult you, but it's easy to get backwards, and is pretty important
If using a sunshade (ever) it will add several inches at the objective end, and will continue the down angle of the scope relative to the barrel, which may require slightly more ring height.
All that said, many ring makers provide actual measurements of their rings' height, so if you measure yours from base to center of the tube, and then subtract the barrel-to-objective gap, you should be able to select the correct height rings. Be sure to go a bit high rather than low.
As has been said, fitting you is more important than anything else, so if your eye is behind the center of the eyepiece when in position, you have the right rings, regardless of the gap at the objective.