#1> Is the heat pump directly under the radiator or off to the side?
#2> Instead of just folding the excess back, be sure it is wrapped tightly on itself for two or three close turns (like a hangmans noose), then let the remainder hang free instead of wrapping it back on the radiator.
#3> Can you give me SWR readings at:
#4> What are you using to measure SWR?:
antenna analyzer,directional watt meter, rigs internal meter etc.
The more information the more we can help.
73 for now,