That's just it.. the holster isn't causing the ND, it's the person drawing the weapon and putting their finger on the trigger before acquiring the target. A proper draw will not have you placing the finger on the trigger.

It really comes down to building muscle memory. Luckily I work from home and I can practice drawing 50-100 times a day. I practice both concealed draw with a t-shirt or jacket covering my weapon (unloaded) and I practice as if I were open carrying. Just to build the muscle memory that will take over in a crisis situation. It was the same reason we practiced over and over in the military.