I've always had a problem with binding keys to the reset function. I was able to bind both shifters so that it would reset if you held them at the same time but that only worked sporadically for me.
I've stuck with ctrl/spacebar ever since and that's been working ok.
On the odd occasion that nothing has worked, I've used the steam vr drop down menu to reset seated position.
Mine has been working in the menus and once I've selected "start race". But since the last update, it doesn't work if I'm in the pre-race menu. Not the greatest, as I prefer to line up my wheel prior to taking the grid.