I don't think they're exactly compatible with the shift boot.
Obviously the thread is the same, but for the ST (and I'd assume also for the Sport), the shift knob has a glued-in plastic ring at the base with two tabs to lock into the boot ring. And there isn't a lock nut to adjust the height of the knob, you have to screw it down as far as it will go.
I went the other direction from you - I tried to use a 9th gen Si shift knob and a 2007 Acura TSX knob (having both on hand) with my ST, even with a small plastic ring to catch onto the shift boot, the two knob didn't "line up" quite right. They went like a quarter turn too far. I had to use a few washers in lieu of a lock nut to raise the knob so it's look right.
So in the other direction, if you used an ST knob with your Si, I'd imagine the opposite: the little plastic ring with tabs would have nothing to hook onto.
I took a few pics of this when I did it back in Dec 2021
in this thread