When I'm wearing shoes with 1" thick souls, it turns out I can comfortably sit flat footed in a 30" perch, though it is less deep that what some would use at 18", 6" deep instead of 13". The bottom of my glutes are 33" off the ground with shoes on.
So now, my only reason to not want a 60" fl dob is the narrower view at lowest power or needing a big, heavy eyepiece.
My target now is 16" f3.4 with a 20mm 82 deg eyepiece and budget coma corrected that leaves the outer 20% a bit comatic. I could sit at zenith with a 20" chair, and have a 1.2 deg fov to see beginner targets in the frame I want.
A 30" chair could comfortably sit 18"-19" f3.4, or 20" chair and f3. Between coma corrector magnification, extra coma and weight at 100 deg, faster objective, narrower view, it seems that 18" is more of a specialized or advanced scope for people who no longer need to see the beginner targets in that frame and want to zoom in or save them for a much smaller scope.
Edited by stargazer193857, 12 November 2019 - 11:33 AM.