Help me prevent counters to my deep half guard

I need some deep half guard help

I feel that I time my shoot nicely. All at once, I get one arm under their leg, the other across their lower back. Also simultaneously get my head deep, close to their hips. Despite this, more often than not my opponent will just reach back with their arm, scoop under my chin, and start choking or bring my head/torso out and start crossfacing. I have some theories:

  1. I'm not as deep as I think I am (obligatory that's what she said)
  2. Maybe I'm not on my inside shoulder enough? Perhaps my outside shoulder is not truly outside, making it easier for them to grab my neck and flatten me out?
  3. Not enough active upwards pressure with my underhooks to get their upper body away from me and forcing them to post?

Am I missing anything? Or am I conceptualizing this all wrong? I'd love some tips. Everyone in my gym has at least 25lbs on me and I also have zero muscle mass, but I'd like to believe that technique corrections alone can help me here. Maybe I should quit all offensive work and just become a pin escape savant lol

EDIT: After a few replies I think I’m maybe misinterpreting what “deep half guard” is… to be more clear, I am simply talking about this position https://imgur.com/a/gPErIYS. I can get to this position, but have never been able to progress further