To get the real nose measurement you could take the cam lobe base circle diameter, divide by 2 and add the lobe lift, this would give actual R value I think. Once plugged into the remainder of the calculation you provided that would give you a precise measurement of the distance covered at the nose for each crank degree rotation.
You could do all that but I overestimated so much on the numbers that the end result would be significantly less than .070. Just not worth the hassle IMHO. i.e. if you have a 1" dia. base circle and a .750 lift cam (1/2" lobe height) you end up with .043" travel for 5 degrees of cam travel. You won't see any movement on a dial indicator at max lift. And the smaller the cam the less travel.
