You may wear your shirt untucked as much as tucked. The shirt needs to be versatile and look right however you choose to wear it. If the shirt is too short and you reach up, the shirt may come untucked. If too long, the shirt loses its style when untucked.
In designing the Todd Shelton shirt, we found our balance for both uses: long enough to tuck, short enough to look right untucked. Notice Paul (6’ 1”) in the picture above, you can see the shirt length and hem shape we endorse.