The 20x1's are long enough where they will work but have to be cheated like you were doing. I like to remove the front slide plate and watch the needle, thread, and shuttle with a flashlight and tilting machine. If you figure 1-15/16" Davis long length minus the length of your 20x1 will give you a rough figure you need to lower needle. No cheating with Boye 10 but there costly per needle.
Jon
Jon