Maybe I'm not looking at it in a very pragmatic way, but if I recall my thermodynamics of boiling liquids:
(Rate of heat absorbed from burner/coil) = (Rate of heat lost to ambient) + (Rate of heat used in vaporization of liquid)
The term on the left is a function of burner power (easy to tweak) and setup geometry.
The first term on the right is a function of pot geometry, ambient temperature, wind speed, etc., and is not-so-easy to tweak
The last term is directly proportional to the boil-off rate.
(Note that this equation only applies to the steady-state boil, and not the temperature rise of the liquid up to the boiling point.)
So if you want to reduce the absolute amount of boil-off, reduce the burner power until just barely at a boil?
However, I do agree with others who have posted that consistency is the key aspect to the process.