I did a nice 6-inch F/12.5 about sixty years ago! One of my first and it was a learning pleasure and great performer.
You'll get a superb figure pretty soon. The good news is that a 6-inch F/11 will be a piece of cake to get right. Perfection is nearly spherical, so forget the Ronchi and just use a common traditional knife edge.
1) First, work the polishing simply and gently until you get a complete polish --- with no testing at all. You will need to get that rhythm where the action feels viscous and smooth drag and just hang in there, entirely by hand, for a few hours. Then give it an extra hour just "for good measure". Don't overthink it and lay off the obsessive testing.
2) Next, polish very conservatively center over center with slow deliberate, shorter stokes c/c, maybe some W, and more rotations than before. About half an hour. This will reliably drive the figure toward spherical. No testing yet - don't cheat.
3) Rinse the mirror off and let it stabilize in your testing environment for a couple of hours.
4) Now take the knife to it. It should be very close to spherical with no edge problems.
5) Do the figuring in the traditional manner to coax it to a perfect sphere --- smooth, bland, boringly wonderful. Nearly all of your time will be working other mirrors, as the six-incher comes to testing stability. At this stage nearly all of your time will be waiting for meaningful stability. Figuring runs will be very short --- just a few minutes each.
6) Now that you have a perfect sphere --- parabolize it in very short runs. To take a 6-inch F/10 from a perfect sphere to a perfect paraboloid could well be just a minute or two on the lap. It's very easy to overshoot, so don't get too aggressive or anxious.
That's really all there is to it! Assuming that you glass substrate is superior (e.g. fine annealed Pyrex) things should go quickly. The wait-times can be doing other mirrors or reading a book.
I watched the professionals doing this kind of hand-figuring work at B&L back in the 1960s. German artisans from the Old Country. A good optician would knock off around half a dozen superb mirrors in an 8-hour shift, without even breaking a sweat. I only did my hobby stuff, so could spend days or even weeks on a mirror. Tom