I'm using a Brother QL-1100NWB printer and generating 4x6" shipping labels with the iOS Shopify app. Unfortunately all labels printed through Shopify cut off about 1/8" of the bottom, as though the printing starts further down on the label than it should. Normally it's not a big problem but when printing USPS international labels it cuts off the "quantity" values on the customs area items list and I have to write them in manually. It's annoying, and it doesn't happen with other things like PirateShip labels.
I don't see any way to adjust the zoom level, nor to adjust the alignment of the paper - though it only happening with Shopify leads me to believe it's not the printer doing it but the Shopify app not sending the labels at the correct size or something.