Why do "fn ->" and "fn <-" behavior differently on T470 & T480?

I have a T480 and a T470, both running Ubuntu 18.04. On the T480 "Fn ->" and "Fn <-" move the cursor to the end and beginning of the line. On the T470 that combination does nothing, I have to reach up to the Home and End keys. I can't seem to create any custom key combinations with the Fn key at all on the T470. I've tried using xdotool as suggested here with no luck as the custom key binding interface doesn't recognize I am pressing the Fn key.

What's the difference, and is there any way to align the T470's behavior with the T480?