You have an outdoor sensor/thermometer?

Yes, I have an outdoor sensor

I would say you probably would have to remove a wire off the stat that fires the furnace for defrost mode but I bet your going to run backwards and then try to gain yardage.

When defrost kicks in the heat pump reverts back to a/c mode and takes indoor heat to thaw the pump which adds a tremendous amount of cold air into the home. I know this because I had a unit that the installer forgot to connect the defrost. I am not sure if there is an option to reduce the burn rate during defrost which might be an option to look in to.

I have a demand defrost Rheem/Ruud that rarely runs a defrost cycle unless it is humid.. freezing rain or snowing. In these conditions I can have more than the average time cycle defrost.

Also the stat should have nothing to do with the defrost cycle unless I am having a brain cramp.

You can try the control board however, there are fewer chances that it will prove to be any help. As for your propane bill, it could be ironic of me to ask you to check for any leaks, which I assume you have already done. That leave you with the user manual, which is not proving of any help so it would be better if you call the company to send their technician and check it.