i might of been able to reach. I know I have flexibility issues in my drysuit. I did not really understand the problem while I was underwater.
I definitely understand the feeling. When you're surrounded by equipment, a dive-mask, etc many things become far more difficult complicated and confusing. Flexiblity changes, visiblity changes, and items when the harness is unequipped aren't exactly where you might expect when equipped.
When I first switched to backplate, it took me a few weeks to realize why I was having so much trouble finding where all of my clipped-off gear was while underwater. It's easy to forget (or not realize) you have zero core-flexiblity with a full backplate. Since then, I've started practicing on land, in my gear (including mask, usually minus the tank(s)), reaching for various equipment, d-rings, straps, etc without looking so I can
consistently find and clip off items. I also used this for finding better locations for gear. I've also carried this over to my sidemount setup, where I try to practice doing things without looking.
It's not 100% identical to what it's like during a dive, but it's also lower-maintenance, and you're not using limited air or dive-time to do that practice.