No problem. OK, if the new hallway is five feet shorter, where do you want the kobolds to go? If they are squeezing, however that works, I can probably replace their icons with two lower-case ks.
For Point of Origin, the basic rules do say the point of origin is included in the area, so I guess that could work. I mean, it would mean that, with a 20' radius, a PoO that is in the middle of a square would technically cause the spell to end halfway through a square, but there aren't rules for that in 5e. Since they go with simpler is better, I think just saying the thing has a radius of 22.5 feet works best. It's easier to map.