I flew LCY - GLA on Friday night (E190), prior to boarding they announced the usual "flight very busy, smaller bags under your seat" etc. and asked for volunteers to check their bag. I volunteered, and had my boarding group "upgraded" from 3, to 1. After a few volunteers, they again asked stressing they needed four further bags in the hold. Not sure if they got them or not.
Once boarding was completed, I was surprised to see quite a bit of spare room in the overheads, maybe 15-20% spare. I reckon everyone's bags could have made it in. But I don't suppose they knew that before the announcement !
My regular sized wheely certainly would have done, but sideways, rather than wheels first, as has already been pointed out.
I like the LCY Embraer flights, great legroom, and you still get a drink and a snack ! LCY itself was chaotic though.............. 17:30 on a Friday.....
Bag appeared in GLA at the carousel with a "Priority" tag on it, not that it came out any earlier.