Try asking the horse to come into and outline, then give more rein to allow the horse to strech the outline (but don't lose the generall shape), then shorten the rein so the horse is working oover bent.
Repeat this about 2 times
Next as the horse to go long and low flexing to the right and then ask for over bent flexing to the left, then over bent to the left and long and low to the right,
This is exercising all the muscles in the horses neck and allows them to warm up properly.
If this routine is used as a warm up everytime you ride you will find you and your horse find a happy medium. Which means that your horse works in an outline at the correct hieght, once this is established indroduce collecting and extending your gates, this allows the horse to work out for its self were his balance is and were his head wants to be to work effectivly and comfortably.
Once the horse understands this you will find that the rein in which you ride is natuarlly slighty longer than what you rode with before, also the horses mouth become like feathers and at the your in perfect unison and are in control of your horse.