I think dips like this (performed by jim wendler) are shit, got to get that range of motionThe dip can be a troublesome exercise for some.
i think three mistakes are made;
1. the bar width around 700mm seems to be the best for most, unless you are extremely wide or narrow shouldered
2. Going too low and bouncing out of the "hole" so to speak
3. Like the bench press, No scapula movement
treat it like a bent over pull, as you pull the bar to your torso squeeze the scapular together
fucking ego lifters