I'm not sure how that is giving you a range when it is based on other percentage stats? A range would indicate a list of hand types a player would play in this situation, but you can't get that list from percentage stats.
You seem to be subtracting the percentage of 4bets from the percentage of 3bet calls, when you already know the percentage of 3bet calls..
I imagine what you actually want is just "(call 3bet %) * (open raise %)"?
That would give you the ratio of the number of hands with which the player will call a 3bet after open raising, out of the total number of hands.
If that is the case just create a new stat and set the expression to be the expression from "Call PF 3Bet" multiplied by the expression from "RFI".
Tutorial: Custom Reports and Statistics