There are a number of ways around this:

1) reamers are to restore a fitting dimension post heat, not to adapt ill fitting tubing. For one thing, you need to ream terribly deep if you want to conform a whole tube. While with the partial approach, you are only going to need to zap the area you heated.

2) If all you need to do is nudge a tight spot, that is something an adjustable reamer can do since, when it hits full wall size, you will note a different resistance, and can stop cutting, and test it. But using an adjustable to resize a tube is too imprecise.

3) Are you doing this for personal use, or for professional use. Certainly with the latter, as your eventual goal, you have all kinds of other aspects to financing your tools, and for the quality of work that will be expected.

4) I think it's 26.8 that fits standard 4130 tubing. With a lathe you can do some interesting things.

5) You can sleeve tubing and reduce the heat effects to the point where no reaming is required.

6) I use an adjustable reamer, but the reamer quality, sharpness in particular is not equivalent to good bike tools. It does work, I got the idea for it from a pro, but I will probably upgrade at some point.

7) In the amateur context, if you go the 10 dollar reamer approach, you need to plan your whole seat stay approach around it. To the extent you might want to design your stay attachment with no constraints, then you probably need the best tooling possible to restore the fit. That's probably another thread.