try this, the real problem i have with the "lock" position, at either point during the exercise is at that moment of "lock" blood flows into the muscle..
If your goal is size and strength, then you want to keep the muscle under tension, you want to cause micro fractures withing the mitofiber and cause damage to the mitocondria, so keeping the muscle under contraction "anabolic = without oxygen" rather than "aerobic = with oxygen" you will cause more damage and thus increase the possibility of new muscle size, and cause the muscle to increase its ability to hold more glycogen and create the effect of "Mitocondrial re education"
With that said, the best success i have had is to do 3 exercise in straight sets 4-6 rep range, then the 4th exercise for that body part to do 60% in the full range open and close at the top and bottom.. trying for 20-25 reps.. this will pump more and more blood into the now damaged muscle, bringing more nutrients and taking away more of the lactic acid..
If that sounds like too many exercises to you.. do 2 straight sets in the "unlocked" condition, then in the 3rd exercise do the open/20-25 rep range for 3-5 sets.. if you can..
If you can reach above your head to remove your shirt, then you did it wrong..