I just dug up a resolution chart that I have available at the moment. Using that chart, the 24 LPPI bars were resolvable by me at about 70" or 6 feet. Very similar to your experience and I did not know the measurement until I marked my feet on the floor.
Last night I used an inch ruler and came up with about 117", with the same result today with the ruler and that chart side by side in the same light. Doing a more precise than necessary conversion of 3.175:1 for millimeters to 1/8" marks, that converts to about 36".
I previously mentioned that because the 1/8" marks on a typical inch ruler are thinner than the intervening spaces that that may not be the ideal test. My experience is consistent with that and now I would suggest not using an inch ruler.
For anyone interested in a similar chart, rather than relying on rulers...
I uploaded a snippet of the resolution chart I used here. If you right click the image and download it you should get an image with an image size of precisely 75mm x 75mm (or very close to 3" on each side) at 600 DPI. This is the total image size, as reported in PhotoShop, including the white borders around the target. If not, re-size it.
The 24 LPPI bars are circled in red (excuse my sloppiness) just to be clear which bars you are resolving. Technically the bars should be spaced at 25.4 LPPI but 24 is more than close enough.
One of the problems with this test is that there is no clear point when the bars no longer resolve. Anyone familiar with the math and conceptual idea behind MTF understands that resolution is not a black/white idea. If a lens were resolving this chart at increasingly long distances, then at some point the white space between black bars starts "turning grey", indicating a declining MTF, and finally becomes monotone.
This is just to say that people with equal eyesight will arrive at slightly different numbers but my experience is that at the limits of resolution the difference between clearly resolving the lines and severe doubt is only about a foot at the 6 foot range. I assume others would have similar results.
A 6 foot distance on the millimeter test is better than the double star numbers I suggested above but they are different tests with different problems associated with, in particular, the double star test. At 6', the millimeter test is equivalent to 113 arc-seconds (just under 2 arc-minutes) or about twice the resolution of the COC used in standard DOF tables.
It is likely easier, for example, to resolve long lines, which are large integrations of "binary stars". It is not clear to me which better models us resolving a print to the limits. I could argue that both ways . This is the reason that it is very difficult to model or test resolution as it applies to optimum print viewing.