How granular is the 25/50% room mode "rule"

[franktree]

I've read a lot about how you should ideally avoid having your listening position at the 25% or 50% point in a room because that's where room modes tend to be the most pernicious. I'm sure if varies from room to room, but as a general rule, how far away from 25/50% do you need to be to be out of these most problematic areas? Is 26% or 49% okay? Or does it need to be more like 30% or 45%?

I know there's also the general rule (or suggestion) about trying to have a listening position at 38%, but given all the particularities of my room and other variables, I'm not going to get close to that. The positioning that is going to work best is likely to be somewhere between 23% and 26%, so I'm trying to figure out if 26% is basically just as bad as 25%, or if it actually makes a meaningful improvement to move from, for example, 25% to 26% (or 24%), theoretically speaking, of course.

[DanDan]

TTT. Generally 50% will experience a huge null due to the lowest and usually by far strongest mode. At twice the frequency, a strong peak.
Of course we typically sit at half height and half width, a double bubble disaster, but nobody likes to talk about that.....
38% was a mathematical concept enhanced hopefully by occasional proof. It presumes and infinitely reflective rectangular room with Flush mounted speakers. I remember our friend Boggy writing that he often found the Optimum Listening Position at 19%
I think it best to use no rules of them. It is hard to get done, but all permutations of speaker and listener location have to be tried. Start with broad strokes, Pink Noise, Spectrum analyser 20 -200Hz. Quickly rule out the No Fly Zones. Remember no rules of thumb. We often find the OLP is with the Speakers kissing the Front Wall. Test Trumps Theory.