There is no right or wrong where to position a BOSS RC loop pedal.
Two more common locations are:
1.) At the end of your EFFECTS CHAIN before INPUT of the amp.
GUITAR => STOMP BOX or MULTI EFFECTS => RC => AMPLIFIER.
Allows for all sound of guitar and effects to be captured and recorded in the loop.
NOTE: Amp adjustments will affect the looped sound.
2.) In the FX LOOP of the amp if supported.
GUITAR => EFFECTS => AMPLIFIER = FX LOOP SEND/PREAMP OUT => RC => FX LOOP RETURN/POWER AMP IN.
Allows for all sound of guitar, effects and preamp to be captured and recorded in the loop.