The 20 moa base only adds 20 moa to your current elevation from a static point.
Example:
With a 34 mil turret, you zero your rifle and end up twisting the turret 3 turns (5mil per turn) to hit at 100 yards.
This means you have 15mil wasted from total elevation, leaving you with 34-15=19mils.
Plenty to go around, but we want to increase that to 25 mils of scope elevation.
So we install a scope rail or mount that gives 20moa / 6 mils and zero again.
Now we have that 25mils of available elevation.
But the ballistic app does not mind any of that.
It just gives the elevation and does not care if your scope can or cannot do that.
When previously when it gave 25 mils, you'd have to hold with reticle. Now with the 6mil added, you can just dial it all.