The relation between the numbers don't change very much - it does not matter for me whether the DeltaE ratio between the inks is 0.79 or 0.82 , the Epson 106 ink performs consistently better than the HP 31 ink , and the papers remain in different classes.
Let me provide an update to this test after 4 weeks of exposure - the Epson 106 ink and the HP 31 ink both on a HP Premium Plus Photo paper and a Logicseek 250 gr cast coated. I'm reporting an average DeltaE(74) of my profile patch sheet with 96 patches.
106 ink_______4,62 both inks on the HP paper
HP 31 ink_____6.13 which makes a ratio of 0.75
106 ink_______12.03 both inks on the LS250 paper
HP31 ink_____11.59 which makes a ratio of 1.04 , both inks perform about the same on this type of cast coated paper which is quite in contrast to the results on the HP paper. Both inks fade much faster on this LS250 than on the HP paper - 12.03/4.62 or 11.59/6.13 , but the cc-paper apparently protects the HP ink more (in relation) than the 106 ink for some reason. There are some reading tolerances but they are much smaller and are not the cause for this effect.
This shows the complexity of such fading tests and the dependence on the actual test setup, results can differ apparently quite a lot if you change a variable e.g. running the test on different papers - with different inks, and there are other hidden variables with the test setup which I'll adress later.