For a 12 oz. mix, I'll fill a 1/4 TSP spoon full, add about 1/3-1/2 of that spoon to the virgin liquid (un-necessary), I'll cook the batch and after I make the 2nd shot, I'm looking for the level of "smoke" because the smoke is the stabilizer "evaporating" off. After about the 2nd shot, I need to add a little heat anyway, so I'll add a few drops off of the spoon that's holding the stabilizer, mix it in as the heat comes back up. This is actually more stabilizer than is needed, but it's just what I do...and it leaves a bit of stabilizer in the scraps for remelting.
The Softer my plastic is (Soft), the less heat is needed to keep the mix at Working Viscosity, so I can tend to use a little less stabilizer using Soft...using Hard/Saltwater, I'll use a little more stabilizer (as in, a few more drops) because it takes a little more heat to keep it the same Viscosity as Regular and Soft...and yes it's linear, Regular/Medium is between Soft and Hard in the amount of heat that's needed to maintain the same Working Viscosity.