" I've flown a Twin Squirrel at 11,000 ft+ with no doors - no problem but, put me near a cliff edge or on a tall structure and I freeze!"
Thats because your connected to the ground when looking over a cliff edge, hence the perception of height, proved this many moons ago while being winch launched in a Primary glider at Bicester, while on the launch I suffered severe vertigo, got rid of the cable & thoroughly enjoyed the ensuing 20 seconds of free flight! No problem with it on aerotow.
Not looking forward to going up the CN tower next month!