Question regarding proper usage of circuit setters

Can circuit setters be on the return side of the piping or should they be on the supply side, directly after the pump outlet? I just came across a job that needs balancing and the circuit setters were on the return piping, just before they connected to the return main. Do you still get accurate readings with them in this position or should they be moved to the outlet side of the pump on the supply piping? Thanks in advance,
Warm regards from chilly Fairbanks,
Rocky