After replacing digitizer the homebutton sits too low!

The display assemblies you are using do not have the correct corner tab height or your not pushing them down enough. Cheap displays sometime sit too high. You can put a piece of business card under the button or get better fitting assemblies.

it's because Shenzhen made digi are a bit thinner than original. also there's a 1mm empty cavity inside so when you take the protection film from below digitizer the LCD goes inside the frame. if you cover that cavity with a sealer or use a transparent film could be better.