If it's too hot, it will evaporate more moisture - or melt the cone.
If it's not hot enough, it won't melt snow fast enough.....
So, you clearly need something better than a $20 Rain Collector Heater (and a few dozen hours of changing how it's attached).
A few temperature sensors to measure the surface temperature of the cone, and a control circuit, should do it. Just keep the cone surface temperature a few degrees above freezing.
Anything else is a compromise.