I’m about 5’8’’ and I thought that my box was the right height for me and no one else has said anything on my other threads. However, it seems like I’m a bit high on my box squats. I’m not sure, but my hip crease might not be parallel to the top of my knee.
I think you're box squats look fine. You are just at the acceptable powerlifting depth. You're goal is to hit a parallel or sleightly below parallel raw squat right? I wouldn't lower the box, I once decided to do a training cycle like that, I lowered the box height like four inches below parallel, I of course had to lower the weight significantly, I added some decent pounds to this low box squat and when I went to my normal squats I was allot weaker. I attribute this to the lower load not stimulating the other muscles as much, in particular my quads, and/or hips. So if I were you i'd keep the box height you have now, but be sure to mix in regular squats so as your quads do not get weaker, i have noticed box heights like yours do great at developing strength out of the hole but still do not hit the quads. Keep in mind my experience is based off of a wide raw squat.