When I molished a ramp to get barakta in and out of out front door, a wheelchair-user friend recommended the addition of some L-shaped aluminium profile to prevent the castor wheels dropping off the edge of the sloping portion. Having since wrangled a wheelchair full of delicate barakta over it dozens of times, I concur that this is very much a Good Thing.
On that basis, I'd suggest that the key thing is being wide enough for the chair, plus reasonable wiggle room, and then either enough extra width that the edge is trivially easy to avoid, or some sort of raised edge to catch errant castor wheels.
The chair is probably no more than 0.7m wide, in order to fit through a standard doorway. Track width a bit less than that, on account of the pushrims. A 0.88m path would seem quite tight unless there's an edge to bounce off.
OTOH, if you leave a central channel, that's something else for wheels to end up in...