Your formula is twice what is shown in Bearcarver's step-by-steps. For example, in his "New - Canadian Bacon" step-by-step, here is what he posted:
Calculating curing time:
The method I use for calculating curing time is simple.
Measure the thickest spot of all of the pieces of meat you plan to cure.
Figure how many "half inches" there are in that measurement.
Add 2 to that number. That will be the minimum time that I would cure that piece of meat.
Then I personally like to add 2 or 3 more days to be extra safe (you can't over-cure, but you can under-cure).
My thickest piece was 2 1/2 inches. There are 5 "Half inches" in 2 1/2".
So that would be 5 Days plus 2 days = 7 days minimum curing time.
Then I always add 2 or 3 days to that, so I planned on curing this stuff for 10 days.
So his formula is 1 day per half inch of thickness, not 2?????