Very nice Kohaku. Note the glistening in the Hi plate, the even color, and thickness of the Hi. This is a sharp, focused photo... notice the individual scales in the red? ... exactly.
I have two knocks on this fish. The pattern is too simple; and it is not in my pond.
As to your question... I've not read any comments/observations that Hi trailing into the dorsal indicates longevity for the Hi overall. I have read that Hi at the base of the pectoral indicates pigment strength, but I am not aware of any actual basis for the idea. ...no scientific studies to my knowledge. If the idea is based on generational knowledge of koi breeders, then I'd accept it as having some validity, but not necessarily quite the absolute "truth" often asserted. Vogata has posted photos of several Dainichi Kohaku in a couple of threads he began. There is pretty much a consensus that the weakest Hi in the group is the Hi of the only one with Hi in a pectoral. ...So much for the rule of thumb (or evaluating Hi quality by photo... take your choice).
JR has commented on the so-called "white spreading gene". The idea behind it is that a gene (or combination of genes) causes white to appear and spread out over a koi, creating a pattern. Compared to the older Higoi/Benigoi types, the white-spreading gene gives us Kohaku. If the fading of Kohaku to Shiromuji is the result of an "over active" white-spreading gene, then maybe Hi in the fins indicates a less active gene that's less likely to lead to Shiromuji??? Maybe. Maybe not.
I think it better to focus on the quality of the Beni on the body, and not look for Hi in the fins. Studying Hi to understand what you see ... to be able to realize what is thick, deep pigment... that is where we should all focus our attention. There are no shortcuts.
Besides, it is best for all fins to be free of Hi.