I taught my springer spaniel to turn on two pips of the whistle when he is hunting at range limit. However, he now pulls increasingly further out when on open ground and is difficult to keep close. Why will he not quarter the ground in front of me?
Unfortunately, your dog has been conditioned to turn only when he hears the two pips signal. He feels secure waiting for the sound and does not need to watch where you are. The result is that he is oblivious as to how far he is hunting from you. Dispense with the whistle commands and instead teach him to exercise self-control and turn naturally on his own. This will encourage him to begin to look to you for guidance.
Next time you take him out set him off as usual, but do not move or make a sound. I am certain that after three or four casts he will glance back to see why there is no audible contact from you. You must immediately react, drop your hands down and do whatever comes naturally to make him come running back to you. Give lots of fuss and praise and set him off hunting again. Repeat this a few times and soon you will have a spaniel that is not only keen to come right in for a fuss but is also glancing at you for guidance and will begin to hunt much closer