I have cut to 12.5 inches and have a possible problem.
The tube is obviously joined with an epoxy and although I have cleaned out the hardened drips there is a film of hardened epoxy reducing the id of the tube.
It only drops down 3" on the hinged stem rather than 5". Not sure that matters as the height is better than it was and there is enough knee clearance.
What I am a little concerned about is how secure the epoxied joint in the stem is.
Obviously, it has been fine for teamonster, and the chap who built it, and my son in law, an engineer, tells me that aircraft have lots of aluminium epoxied together but i worry