Shooting from a square stance is possible, but will take you more time to get your feet into correct position since your lead (front) leg is the leg used to penetrate.
Do not make the mistake of taking your penetration step with your trail or back leg. This takes up valuable time and smart opponents will be able to read your movements to know exactly when you are about to shoot. You want your shot to be as quick and undetectable as possible—save the time and use your lead leg.
