I am using the HP 3050A J611. I don't use an app though. I just print right from my iPhone or iPad. It prints all the pictures in 4x6. I don't see anyway to tell it a different size. Is there an App for that?
You're using the built-in Photo app. That app won't let you pick the printed photo size. It works best with printers that can sense the paper size in the photo tray. The HP 3050A can not do so. You can use the "HP ePrint Home & Biz" app.