If 1200 sq ft home needs 2 ton heat pump would bigger unit be more effincent?

No when It comes to heating and cooling the rule is a little smaller is better. All heating and air conditioning units are a little under sized to prevent short cycling which wastes energy far more than long run cycles. Short cycling also adds to equipment stress and can actually shorten the life of a system as all the parts are design to run for long periods of time and not for starting and stopping in short periods. Liken it to your car and MPG, you get much better MPG on the highway then through the city because you are not wasting energy building up to speed.