I've had a think about my problems with the S3X. The SA lever doesn't pull far enough, I think. So I've swapped over to a Shimano lever as a test. Fixed gears on a friction shift - what could possibly go wrong?
You damage your other shoulder and wrist?
It'll be reet.
And it was. For whatever reason (and impact may well be one), the gear lever liberated from my Orbit, which I have been using in friction mode for years, when switched to index gives me two positions either end and a long sweep in the middle.
Step 1 Top gear
Step 2 False neutral (approx)
Central section: Middle gear
Step 3 False neutral (approx)
Step 4 (and this is where the sweep angle of the indexing is greater than that of the SA lever) Bottom gear.
Now, I've not given it an extensive test, as I had to stop a couple of times to cough and allow the chest pain to subside, but I did try tentatively standing on the pedals in bottom gear, and starting off on a hill. No slip. Promising.
There's plenty of space in the middle, but, if I put the lever about half way, it is secure, so nothing to worry about there.
I hope this is the end of the problem. Certainly, if the positions are the two extremes and the middle on the Shimano lever, that would be fortuitous, and I'd just use friction. I don't see the cable tension overhauling this lever the way it can the SA one. So long as I remember two clicks to change gear, I'm sound. And, as changing gears most of the time is no clicks for me, that's OK.