I mentioned this in another thread but the main reason you slide into the ball is because you slide/sway in your backswing. This in my case is caused by over rotation of the hips

I think people slide in a misguided attempt to build width. Width is not how far away from the ball the clubhead is but how far away it is from your body

Try and feel in your backswing that you stay centered over the ball (you swing around a stable head and spine) and that only your shoulders turn back. Try and stop your hips from turning with your shoulders and also stop your left knee from collpasing in

Most people will find that cant the club anywhere near parallel becuase they arent flexible enough and indeed the compact swing with a stretch in the back muscles is what you are looking for. From here, you are still centered over the ball and you dont need to slide forward to get back to impact

HTH