If you mounted the pouch correct as on the picture the pouch will not move around.
The pouch itself will of course move since it is a pouch, but the platform is not moving like that.
The platform is moving left and right few millimeter since 1 PALS is 38mm (1.5”) wide and the vertical MOLLE webbing is 25mm (1”) wide, this means you have “13mm” tolerance in the sideway when you add the vertical MOLLE webbing true the PALS webbing. (so it can move 13mm left or right, but you don’t see it or feel it if it happens) The platform can move up and down few mm if you pull the pouch extra, then the horizontal MOLLE/PALS webbing will be squeezed few mm and the pouch can move up and down few millimeters.
Of course, you can adjust the MOLLE/PALS better, but then it is not anymore MOLLE/PALS.
MOLLE/PALS is 38mm (1.5”) wide and 50mm (2”) high: End of story!