I think the variance on sides is intentional, to balance traffic flow at gas stations.

(Imagine a gas station where most cars use the same entrance and have the tank on the same side. Half of the cars would need to do a U-Turn to use half of the tanks).

It doesn't matter which side the filler opening is on because the pump nozzles reach.

I have never seen anybody reach the hose over their car. Not sure why but I'd feel silly trying it. Like 'look at me I don't know which side I should have put the gas in'.