macrocephalopod

I'm not sure what the point of "relative ownership" is. The question is: do bigger companies get more money due to size, rather than expectation of profit? And does this more money create larger price, which necessarily draws more money, etc, ad infinitium. (Until they don't.)

If a fund buys 40 shares of AAPL at $129/shr and only 4 shares of Juniper Networks at $24 apiece, it does not necessarily mean more momentum or price impact on AAPL. If it happens repeatedly, for years, it will mean more impact on JNPR because of relative float differences,

Except the fund would have to buy 211 shares of AAPL vs 4 shares of JNPR. AAPL is ~10x10 on the screens (obviously more depth can be tapped) while JNPR is perversely 15x15. Impact on AAPL almost certainly higher.

I expect you’d be of the opinion that if a fund bought 100k AAPL and 75k JNPR every day for a couple of years, the imbalance would be felt the other way (i.e. more impact on JNPR) eventually, despite what shows on the screens and the lop-sided dollar amount.

of course

So then the only question is how does one calculate where the break-even impact is between two stocks in dollars, % of float, gross positioning of active, and the on-screen BBO.

Far from only question, but directionally yes. As I've noted elsewhere, "It's complicated"

I’ll agree with that as I too have said, but I do believe over time it’s closer to relative percentage of float being purchased by price-insensitive buyers than it is absolute dollars. And over the space of a day or five, there’s likely an ADV/float factor which plays a role.