More socketing confusion

[Crystalion]

Okay, before this was just a curiousity to me, but now I'd like to resolve it (because it affects my realm play).

I grok the caps on sockets from drops due to norm/nm.

I grok that Larzuk does the max sockets he can.

I grok that white vs. blue vs. yellow/gold/orange has a limit.

I mostly grok the itemtypes.txt caps on sockets in addition to the weapons.txt cap in addition to item size cap.

But about this last one, I clearly don't grok the 1/25/40 distinction...

Because I thought those referred to ilvl, and I've (again, as I did long ago) shown, via mod test, that ilvl 40 Crystal Swords/Dimensional blades cap at 4, only getting 6 sockets at higher ilvl (e.g. 99 works just fine).

Why is this? What am I missing here? What is the needed ilvl for a 6 socket Larzuk of a Crystal Sword? (I could find this empirically, of course, by binary search cubemod, but I prefer to understand it).