Make sure you time the button presses so they are always the same length apart. The space you put between the first Short and the second Short should be the same space you put in between the second Short and the Short + Punch you use to activate the Super. It’s not a Buffer, so don’t do it quickly like a Buffer.
The Overhead kicks are useful only in a Blue Moon. They work REALLY well on people who aren’t used to them, but on most players, it doesn’t do much for you, especially if you abuse it. So save it for those key moments, like finishing someone off or hitting them when you know they are one hit away from a dizzy. One good tactic is that you can hit Gief with it as a Meaty at a range you cannot be SPD’ed! If you learn that distance, you can usually get a dizzy off of Gief if you land Jump Fierce XX Air hurricane Kick into Crouch Roundhouse. One overhead there will cause Gief to fall Dizzy a lot, and if they try and SPD, you land the kick for sure.