When you look at those 4 in the 20's (UL, UK, Ark, BYU), all have 6 losses (except UK has 7). The quality of losses is similar, although UK losing at home to Missouri may be the worst.
But at the same time, UK has more "quality" wins.
Ark has 4 (in order best to worst) Texas Tech, Vandy, UL, UT
BYU has 4 Clemson, Wisconsin, Miami, Villanova
UL has 3 UK, at Cal, Indiana
UK has 5 at UT, at Ark, St. Johns, UT, Indiana
When looking at that, Ark is 4-6 vs quality opponents, BYU also 4-6 (but 5 of those 6 losses were very high quality), UL 3-6, and UK 5-7. We simply have that extra loss because we played 2-3 more quality opponents. Based on these data, I'd rank the 4 BYU, UK, Ark, UL.