About 60 miles apart for two of 'em relative to the rest of the population
I doubt there's any hard and fast rule about wider or narrower as the amount of V and several other factors mean trial and error is the only way to optimize your trailer. There have been several good points made on what to watch for when moving the rollers but it might also be worth checking none of the rollers are binding as that will slew the boat as it comes on to the trailer. Just see if they all spin freely next time you have the boat off.
I widened the swinging rear rollers on a Rollercoaster 5 trailer last year and found I had to add a keel roller on the axle to protect the keel during launching/recovery. Mountings seem to be provided as standard for just this purpose.
If you do find the boat misaligned on the trailer, I've found you can make a small correction using a ratchet strap sideways off the ski eyes or even the bottom of the engine transome mount. Works best when the rig is still wet and be careful you don't pop rollers off with brute force.
Apply the strap, tension it and then even a fractional bounce the boat on the trailer should move it across. Use any natural slope in the car park in your favour too.