I’m riding single speed. It’s not a steel-framed fixie and I do not have any tattoos, let me explain…
I use a nice but cracked old carbon frame on my trainer with minimal components I hand down from my road bike upon replacement. I have no front deraileur on and the back deraileur is “neutered”. I jammed a socket driver bit in it to lock it to the 17t and run just the big ring up front. There are no shifters; i found some cheap brake-only hoods on Amazon that work great. I do have a 60mm deep dish carbon aero wheel up front that is actually cracked. I mention that just for visualization purposes; it looks awesome 
Anyway, I chose the gear i use because
a) in erg mode it does not matter; I just ride by cadence and step through different power requirements
b) in gradient mode, this gear combo puts me right at about threshold power at 90rpm. This means I can FTP test with it and if I have a crap test I’ll only be able to ride 85rpm and if I get stronger (one day!) I’ll ride 92rpm and more watts. If I get REALLY stronger and one day test at 95 rpm, I’ll consider moving to a smaller nut-driver socket so i can go to the 16t.
This is interesting and relevant because my cadence and speed thus correlate pretty linearly for a fixed gradient, or you might say for a fixed power my cadence and the gradient vary inversely. This combo strangely worked fine through the entire Zwift Island loop. the 9-10% gradients brought me down to, I’d estimate, ~60rpm, but that is not at all what I would expect on the road. I’d expect this gear ratio to be completely impossible for me on a 10% grade on the road. My power was in the 260-300w range at these times so it wasn’t that I was killing it. This was weird. It makes it feel like we aren’t dealing with just simple gradient mode on the Kickr. Yeah?