plyometrics

If you have been in fitness long enough you have heard of a plyometric or a plyo for short.  A plyo is a method used to gain muscle strength.  It utilizes the stretch-contract property of the muscle to produce greater force.  Such activities include jumping, bounding, hopping among others.  However I have recently asked the questions:
1. Is a plyometric basedon the range of motion?  In other words, is an activity a plyo if only 5 degrees of joint flexion os achieved prior to the contraction?
2. Does the strength of the contraction matter?  In other words, after the stretch, does the muscle have to fully contract in order for a plyometric effect to occur?
3. Does the movement have to be voluntary?  In other words, what if the stretch and/or the contraction is a reflex?

Just some things to consider when attempting to come up with strengthening techniques for someone who may not have full ROM.