||So is your question around the trigger wheel itself? Or the mounting of the sensor?
What would be excellent (IMO), would be some kind of telescopic (think upper control arm threaded sleeve) sensor mount, that when combined with a threaded Cherry sensor (or the like), gives a stack of 2 axis adjustability for the sensor tip placement, therefore covering not just the ATI, but Ross and all the other alloy balancers on the market.
Back to the question though, as long as the sensor (or wiring) is not in direct firing line of a broken accessory belt, outside the lower timing cover gets my vote.
Having said that, anyone who is going this far is probably going to be pulling the engine, and can mod the lower cover.