I think I know what the issues is. Bioshock Infinite is the only game I've ever encountered where the WPS setting doesn't scale to the Windows norm, i.e.
6 = 1/1
5 = 3/8
4 = 1/4
3 = 1/8
etc
Instead it's:
6 = 1/1
5 = 0.8
4 = 0.6
3 = 0.4
But the code currently only supports the Control Panel WPS values (1-11), there are gaps for the registry config which are missing. I think that's what's throwing the calculation off.
I'll take a closer look at this, they might even have changed the scaling since it was first analyzed for all I know.