Calculating total position risk while scaling in?


All in = cash available * 0.02 (risk for the trade) / stop distance
Scaling in = A portion from all in lets say 1/4th

When you go all in the first time a condition is met its easy to calculate risk for the trade, which on a per share basis is the stop distance or at the position level is stop distance * size.

But how do you calculate total position risk when you are scaling in? Is it a good practice to consider the avg buying price - wherever the stop is as your avg risk per share while scaling in?