Not I; been there. I just made a 180 when I got halfway across the parking lot…
Yes, it can be done on a 6 footer, or even higher. I have mastered it on the 6’ but don’t make it every time anymore, because I don’t do it much.
NOTE: Running mounts, especially on 6’ or higher unicycles, put a lot of stress on the frame. I bent my original Schwinn Giraffe seat post practicing running mounts. Fortunately the frame has been unscathed all these years.
The hardest part about the running mount is coordinating your foot with the pedal, while at the same time committing all that force to it. The amount of force depends on your height & weight vs. the height of the unicycle, and the higher any of those is, the more force it must be.
So I recommend people practice by getting the foot and the pedal comfortable with the meet-up before trying to go all the way up there. Do this on concrete or another grippy surface. Linoleum is kind of the opposite, and likely to end you up with lots of tire skid marks on the floor.
I worked out a timing mechanism, which I believe is mostly in my head, where I would count to three while watching my dominant pedal come around, and go for the jump on the third pass. This allowed me to coordinate my feet with the pedal rotation so I was able to make a good jump by the time I got to three.
Try not to make the unicycle do all the lifting. If you combine upward with forward momentum, it will be an easier lift. Then, like a kickup mount, you will tend to end up with your dominant pedal at the bottom. This is how I finish, in the dead spot and not all the way balanced yet. No problem, pull the other pedal back (or if necessary pedal backward a rotation or two) and there you are.
Safety equipment, including leg armor, couldn’t hurt during the learning process…
I eventually learned the running mount to a one-footed idle (other foot never touching the pedal). This was what put the tremendous strain on my frame and bent the seat post. You should be fine with regular running mounts and giraffes with good, rigid frames. I would only worry about lower-end giraffe frames, though most of todays, including the Savage, are probably fine. A-frame or not, the stress is mostly on the part above the pedal area (bottom bracket).