I've never trained a gundog but have trained my Brittany for Falconry purposes, which is more or less the same without the retrieving.
I only use 3 variations of whistle in the field. 3 blasts means 'come back and sit at my left hand side', 2 blasts means 'work back towards me' and 1 blast means 'work the opposite direction to the one you're working now', so effectively I can control the distance she ranges from left to right.
I incorporate these with hand signals also. 3 blasts is arms wide open, nothing for 2 blasts, and 1 blast is either left or right arm out depending on which dir