Your drilling operation should have an approach move. The Z value of the approach move will be your Z return value for the G98.
the simplest approach move i have found is the Engage/Retract in the drilling operation (you may need to put it on the default interface from the Customize dialog). It already knows the drill point and tool axis and rather than creating a point, you choose the distance. this is especially useful when drilling on cylindrical faces where the point is not on a planar face.
In the cycle parameters, for rtrcto, use 'auto'.