On non-tour models it is always side stand unless you’ve added the optional center stand. Personally, I don’t like center stands, except for some maintenance tasks. I appreciate that they made it optional. Less weight. More clearance.
I pull up to the pump, straddle the bike, even with a passenger and then fill up. I don't get off and keep the bike upright so that the tank gets full to the bottom of the filler tube. I will sometimes deploy the side stand in case the bike should tip over while filling.
I get off the bike and use the side stand. In another thread, a nurse told the story of watching a motorcyclist filling up While on the bike. An accident occurred and the bike caught fire. The rider couldn’t get away from the flames and was injured. Good enough story for me to get off the bike.
I don’t worry about the angle of the tank. I fill to the bottom of the filling neck and know I am still below the recommended fuel level when the tank is level when riding.
Fill it to the bottom of the neck, by whatever system you currently use, then move the bike to the other position and view the level in the tank.
If it's even with the bottom of the neck with the bike upright, when leaning to the side the fuel will still be at the bottom of the neck along the centreline of the bike. (or very very close)
The low side a little higher, the high side a little lower.
Regardless of the method you use, don't overfill.
Especially if close to home and it will soon be parked in a location where it will get warm/hot and the expanding fuel could poison the vapour canister and/or release fumes into the parking area. (we've had threads from posters that have had both issues.
Always center stand when fueling. I used to stay on the bike holding it level until that one time, when something happened that made the nozzle burp/spit that splashed gas on my legs. I think it was a faulty pump nozzle but, once bitten twice shy..
On my '08 I fill it up while still on the bike but on the side stand. On my '18 the fuel filler is way too close to the seat and the jewels to risk it so I get off. I cant believe putting it on the centerstand can make a measurable difference on a bike that has a 200+ mile range.
Here in Kalyphornya we have these big vapor recovery goofy wazoo gas nozzles. I like to pull the things back so I can see the fuel get up to the filler neck on the Wing when full. Not just jam it in and let it shut off automatically. These wazoo's have a tendency to hold gas and spill it out when removed from the fill neck of a vehicle. So I see them as a pain in the asstroid! So I fuel on the side stand and standing next to the bike.
Out of state, it's nice to fuel up with a normal gas pump nozzle. Well, at least in most places.
I used to fill up while sitting on the bike, just pull up and start pumping but so many people drove off without paying that you have to prepay at most of the stations around here now so I've got in the habit of pumping on the side stand. If I'm close to home I just fill it to the bottom of the neck but if I'm going riding I top it off to about the middle of the neck after it has stopped bubbling