This is as much on you as it is on them. Especially if you're the "lead" diver
The only blind spots are those you're not looking. I teach DM's to guid and I've very good at being a d!ck and hovering right over their tank just behind, and watch them "panic" when they can't spot me, them we go back over head movements and area scanning
If you lose sight of a diver it means you're not checking frequently enough. They don't move that quickly
Bad stuff happens quickly. Years ago my wife gave me a post dive tongue lashing (not a euphemism) for not checking on her for 6 minutes - lesson learned
Defaulting to the "I'm alright jack" position probably means you're a long way off from being ready to lead others or being a dependable team mate.
What you need to do is remember to keep your buddy in your sights frequently. Take a shot, look take a shot, look. You're getting "target fixation/task loaded" what else aren't you checking or aware of? Your own air? (extreme example)
Try to get into a routing. Buddy checks aren't onerous or long, once you know their position, they shouldn't be drifting off too far too quickly unless they're on a scooter.
Try to get a routine and not fill your mental bandwidth to capacity