I'm preparing to put down tile in a bath area, and I'm having to do a substantial amount of floor reinforcement. Yesterday I pulled up a bunch of plywood to box off sections, and was able to see a good portion of the plumbing. I noticed the toilet flange does not have floor joists on two sides (the left and right of toilet) as I was expecting. It's simply sitting in the middle of a section of plywood. The joists in the area it's in are on ~28" centers. It is nearly centered between these joists, so the flange center is about 14" to either of the two nearest joists (front and rear of toilet). I have to cut up this area and box it off so it will support tile, but what should I do about the flange? When I box it off, how close to the flange should I put the boards?