Floor joists near flange

[gbh]

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?

[hj]

The flange has nothing to do with the joists, headers, or anything else. The last thing carpenters are concerned about is where the toilet will sit so they can install a joist next to it.

[gbh]

The last thing carpenters are concerned about is where the toilet will sit so they can install a joist next to it.

While building my house, I'm sure the only thing the carpenters were concerned with was "How long until beer-thirty?" Poke a hole in any wall/floor, and it is all but guaranteed you'll find a quality control issue. In any case, shouldn't there be additional support for a toilet rather than simply placing it on an open span of 3/4" ply? I'm going to beef up the area some in any case, I just thought there might be accepted standards.