You may have more luck with the newer version of the device handler that @zcorneli released, there’s a link to that DTH’s thread earlier in this thread.
I updated my original DTH that Mitch developed to the newer one when I started using @arnb’s SHM delay smartapp.
The newer version of the device handler also doesnt seem to have an option for negative temp offset, on iOS at least (I just checked my own). But you’re more likely to get a response in that thread. His profile page says Mitch hasn’t been to this forum in like a year.