A snug strap should not allow any slack. It lies in a relatively straight line without sagging. It does not press on the child’s flesh or push the child’s body into an unnatural position.
How to adjust the shoulder straps height?
Disconnect the shoulder straps from the metal harness plate located at the back of the car seat.
Pull out the shoulder straps from the front and remove the shoulder strap pads from them.
Thread the shoulder straps through the appropriate shoulder strap slots. IMPORTANT! Shoulder straps must be routed at the same height or slightly below the child’s shoulders.