I would think that GretagMacbeth & now X-Rite would & should (do?) know their own creation better than anyone else. Gretag invented/created/designed the i1 & therefor one would guess that the designers know what is the most suitable size for their device & I would just about bet my house on it that they have done extensive testing to discover the ideal patch size.
The ISO specification is just that - a specification, not an absolute “this is the ONLY way to do this & no-one should ever question what we decide. Just follow us blindly”.
I have tested this myself with my i1 Rev A & using X-Rite ColorPort 1.54 I can safely take my patch size down to 7x7mm (width x height) without causing any mis-read rows/patches. If I take it down to 7x6mm, the rows are too difficult to scan as it very tricky to get the backboard ruler into the exact correct position for the row so that none of the patches from the row above or below the row I’m trying to scan get (mis)read. I constantly have to repeat the rows, sometimes taking 3 or 4+ tries before the row will be read without errors. The size also affects the speed which I can scan each row but I understand the newer i1 devices, such as Rev D, are much less sensitive to this & can be used to scan rows a decent bit faster than my old Rev A.
Incidentally, the i1 IO is much faster than anything that can be done by hand, no matter which i1 is being used. To me this shows that the robotic arm of the i1 is (obviously?) much more accurate than hand scanning. And I always read my targets a minimum of 2 times to make sure everything is consistent between measurements & more often I measure each target 3+ times, again for accuracy & to average the measurements.
I agree with Pat - simply try it out for yourself using your own hardware/software & see what works best for you. The ISO create standards for the entire planet, not 1 person so what might be best for them may not be best for you, me or anyone else. It also doesn’t mean that just because they have created a standard that what they say is the absolute most accurate way something can be performed.
What do you do when 2 standards organisations create conflicting standards - who do you follow or trust? What is ISO says 8.4x8.4mm but NIST says 7x7mm & the manufacturer says 5x4mm - 10x12mm? These are all fictitious numbers but hopefully you understand what I’m saying.