Would there be any problem with mounting unit heater at a slight downward angle to get more air blowing down. Planning on mounting in shop near ceiling peak at app. 12ft above floor.
Just follow the instructions and add a down ward facing baffles. Unit heaters are designed to be installed and operated in accordance with their instructions. Anything else will be out of compliance.
I suspect it would work but I personally would not. My 80k Mr. Heater is installed level and I use the louvers to direct the hot air down. I also usually run a fan to help move the warm air off the ceiling and back down to ground level.
Mine is mounted close to the 12 foot ceiling in the corner! I have a ceiling fan that moves the air around the rest of the building. I would recommend keeping it level!