When do oaks develop a root flare?

I’m growing a lot of trees from seed, as many of you know. Most of them start showing some semblance of a “root flare” by the time the trunk is around an inch or so at the base. Some, even smaller.

Except oaks. I’ve got 1.5” caliper oaks with no discernable “flare”. They are not too deep, because the soil only goes just above the place where the roots start coming out, where the trunk becomes taproot, but it seems like these are tiny roots that don’t have the size to make a “flare” – they’re only an eighth of an inch or so in diameter. The larger branching roots are further down, four, five inches under that point, and even that is only due to the taproot forking from the air pruning pots they were in.

Is that normal? Will those filamentous feeder roots eventually grow into thicker lateral roots?

My Metasequoia, OTOH, also only about 1.75” caliper, already has a gorgeous little root flare going.