You have to back it up 1/4 turn .
The big holes provides the venturi jet and one of them has to point down the horn.
You could even adjust the spring tension in the second stage by backing the HPR out another half turn after that (or even a full turn). But, it has worked well by just screwing it until it bottoms out and then backing it out until it aligns the venturi hole with the horn.
Then you use the two tabs with the screws to lock it in place.
The HPR is not designed to bottom out. It was never intended to bottom out. The original second stage was also not designed to bottom out.
The side smaller holes are bleed holes. They allow air to leak into the case to avoid excessive venturi effect and subsequent uncontrolled free flow.
The amount of venturi flow can be adjusted by partially blocking one of the bleed holes, but just start by getting it working and we can talk about fine tuning later.
Take a look at this thread:
I posted a lot of information and pictures in the thread. It should be helpful to look at it.
Note: when you turn the HPR, make sure to lift the lever or press it down to avoid cutting the soft seat with the volcano orifice.
In the final position the lever has to straddle the IP adjusting screw.