Struggling with Organ Pipe Cactus — would appreciate advice

I want to be honest: I'm not getting great results with Organ Pipe Cactus and I'm not entirely sure why. spider mites in warm dry indoor conditions has been a recurring problem despite my attempts to address it. I've been focusing on providing the sunniest window or outdoor position available based on everything I've read.

extremely long-lived with minimal intervention is there in glimpses, which tells me the plant has potential in my conditions. I have it in a grouped desert landscape display which might not be ideal. complete dormancy in winter with no watering showed some improvement. Two stars for now — not the plant's fault, but not a success yet. I'll update if things improve.