I work under the very basic premise of if you cannot enforce a rule then do
not make it, so why stipulate a maximum start height.

Why do we have a maximum start height at all? Prior to the rules of the
past 20 years the start height for a contest was set at 3000 feet. The
reason for this was quite simple. 3000ft was found to be the maximum height
at which the identifying letters in the underside of a glider wing could be
read from the ground by an observer using binoculars. This was necessary
because competitors had to be logged crossing the start line by an observer
on the ground for a start time to be recorded (There was no GPS) So the
reason for specifying a maximum start height at all is historical and has
no logical purpose if the start is recorded on a logger.
For some reason, after the need for observed starts became unecessary the
maximum start height rule was maintained.
The simple answer to the problem is two fold. Stop using start cylinders
and use a standard D start sector with a start line. Do not specify a
maximum start height, replace it with a rule which penalises any glider
exceeding a specified height before the gate opens, after the gate is open
a start can be made at any height. Easily enforceable, fair to all
including those launching last. Simples