Are you a mathematician?
I would be at the gym all day estimating percentages.
225 working set = warm up sets with 45, 135, 185 (same reps as working sets)
If you were using 315 start at 45, 135, 225, 275
If you were using 405 start at 45, 135, 225, 315, 365
Heavier the working sets the more you need to warm up.(IMO)
I do agree with warming up being subjective to the individual.
If you need more sets then do more sets.