Sometime within the last few years, while playing with Hostargo’s Inverse Dice Mechanic, I realized it wasn’t working as intended. Players were having trouble keeping the GM-called challenge rating (CR) in their head, and remembering to add that after their roll. After some inquiries and minor experiments, it turns out that doing all calculations up front is much easier, so that we can get back to the simple roll vs target number (TN).
So, while we’ve declared subtraction as sub-par, we’re going to flip the system around and say that success is Roll < Stat - CR.
This actually proves useful in 2 ways. First, the player can pre-calculate a target number to roll against (including any extra bonuses or penalties they have), and instantly know whether they failed or succeeded with a comparison. Second, this adds to the feeling of “high CRs are bad”. A level 5 feels way worse when you are first subtracting it from your stat of 8, and realizing you have to roll a 3 or less to succeed.
Ultimately, when working with all single-digit numbers like we do in Hostargo, this subtraction is fast and easy enough to be ignored, and the system flows into the perfection we originally designed!