It may not have to do with sensors or wheel diameter. My gf and I go on rides together both using Strava via phone app. Every time, without fail, the data will claim she rode about .15 per mile more than I, even though we stayed together during the ride. I've tried it with my Garmin and get similar results. I think GPS technology is just jankier than we ...
Looking at the video (the English version I linked in the comments), there are several options for installation. The sensor can act as a replacement for the dust cap found on many cranksets (methods 1 and 2). The dust cap sometime screws in.
This doesn't work if the dust cap and crank bolt are combined (as on Octalink, and similar to what you describe). I ...
The Garmin Cadence Sensor 2 will not pair with an iPhone via the Garmin Connect app, nor directly from iOS Bluetooth Settings. You need to use an entirely different app—I have successfully paired it via Cadence and the Wahoo iOS app.
It seems like it could work using their Garmin Connect App.
See Page 5 below.
See this snippet too:
However, I think optimally this thing is ...