from the CCRs:
15.8 Master Switch
An electrical master switch is recommended on all cars, and required on some, as listed
in the class rules. It shall be mounted so that it is easily accessible from the outside. If
mounted outside the cockpit, it should be mounted in an area where it is least likely to be
damage (e.g. cowling near wipers). The switch shall shut off the motor and cut all power
except to the on-board fire system and any other life support / medical device. The
switch location must be clearly marked. Any marked switch must function as per this
rule, or the indication decal must be removed.
so if the ST/SU ruleset requires the switch, it must be accessible from the outside of the car by a cornerworker - right inside a window opening is probably the "least" accessible area I've seen that passed.