Allowed height depends on situation per F.A.A. regs:
§ 91.119 Minimum safe altitudes: General.
Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes:
a. Anywhere. An altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface.
b. Over congested areas. Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft.
c. Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.
d. Helicopters. Helicopters may be operated at less than the minimums prescribed in paragraph B or C of this section if the operation is conducted without hazard to persons or property on the surface. In addition, each person operating a helicopter shall comply with any routes or altitudes specifically prescribed for helicopters by the Administrator.
§ 91.13 Careless or reckless operation.
a. Aircraft operations for the purpose of air navigation. No person may operate an aircraft in a careless or reckless manner so as to endanger the life or property of another.
b. Aircraft operations other than for the purpose of air navigation. No person may operate an aircraft, other than for the purpose of air navigation, on any part of the surface of an airport used by aircraft for air commerce (including areas used by those aircraft for receiving or discharging persons or cargo), in a careless or reckless manner so as to endanger the life or property of another.
§ 91.126 Operating on or in the vicinity of an airport in Class G airspace.
2. Each pilot of a helicopter or a powered parachute must avoid the flow of fixed-wing aircraft.
Special attention to paragraph d. Pretty much down to the ground if no safety issue !!
Regardless I cannot imagine 600 W putting out a heat signature of such a magnitude to draw undo attention.
If that worried reconsider if you want (need) to grow.