Lift type grips do increase your span slightly, this image shows why.
The wall where the lip is, is thicker.
That's why if your really trying to be accurate on drilling the span, You should know what type and size of inserts the player is going to use.
Then use a set a calipers to measure the wall thickness, so you can compensate for the wall thickness on the cut to cut span. That way the finished span is spot on.