I find the deep mag carriers like this one don't allow me to get enough purchase on the magazine to draw it reliably under stress without fumbling.
I prefer the types that expose 1/3 to 1/2 of the magazine to facilitate a solid initial grip.
^^^^^^^^^^^^ Agreed.
If I can't get a solid purchase with my thumb and middle finger (index finger aligned with spine of magazine), then it feels very awkward (to me) and the effects of 'stress' can not be overstated. Good point.