Is this a concern I should have with the chair?
If you only drive on hard surfaces then it doesn't matter. Fat tyres mostly waste power when at home, turning left/right all the time. Measured. A large difference. But I have a foot of tyre width. In a straight line on the pavement there's very little difference, but there is some easily measured so it makes *some* difference outdoors too.
Drive on grass with the dog any distance, and apart from getting stuck, narrow tyres eat more power rather than less and you end up losing out in range rather than winning. So it depends on what you plan to do. And how important range is.
My BM3 chair has about 45 miles even with fat tyres due to the large lithium battery. And that's with a high speed chair. Where the softer tyre seemed like a good compromise.
The chair I am rebuilding now, has very low rolling resistance. download/file.php?id=4165&mode=view
Because it has a high ply count (6) so is quite a stiff tubeless construction, and because its a radial, and because its a 2 inch larger rolling diameter, and also because its a rounded profile. So only puts its "width" on the deck when on the soft turf/dirt track/snow or whatever. These are fat, and have lower rolling resistance than the stock crappy powerchair 300 x 8 cross ply grey tyres. Add to that, the lack of weight over the casters, lowering turning and rolling losses at the front, the 4x greater battery storage, and the 50lb weight loss from the battery (over a 100lb from the complete chair) and I expect to get MORE than 4x the range of a stock 24 mile lead chair... Will it be as comfortable? I don't think so. But I built this one to look cool!
There's more to consider than just width.