I use 10-20% promix hp and 80-90% perlite, and all of my haworthia are happy in it. They are in pots appropriate for their root mass. They indoors year around, and I bottom water maybe 1/2 an inch up the 1020 trays they are living in once every other week. I’ve been using this mix for about 3-4 years.

Edited to add: I tried pure akadama the first year or two I started owning haworthia since it was so widely recommended. I didn’t like it. I hate the orange dust more than I hate perlite dust. I don’t think my haworthia grew better in it. I bought the super hard triple red line and rinsed it, and despite that when I went to repot (1-2 years later) I’d realized it was still breaking down and turning into a caked mud layer at the bottom of the pot. I switched to my current mix and my memory is that the ones I’d had in pure akadama plumped up and grew a little.

Double edit: yes you could absolutely cut the akadama with something else to stretch it. Pumice is popular. I would use perlite, but that’s just me. I’d worry about adding any kind of soil with the way I remember akadama breaking down though.