Pro's not wrong, don't go after them til you're feeling in! If you're smashing the short ball in the nets then I doubt there's much a technical problem as net surfaces are usually quicker/bouncier than a proper wicket, but sometimes it just isn't worth the risk taking the short ball on. The pull shot is easily my strongest and most productive, but I've played games where against certain bowlers on a quick track I've had to just get out the way of the short ball as it's too risky with the field set. As soon as you figure out a bowler is going to be banging it it, weigh up your options for shots you can play - if you can't find a shot you're happy with then just get out of the way, as I'm sure you know the bowler will go back to bowling full pretty quickly if you don't look bothered by the short ones!
As far as drills go, the best I've heard suggested is aiming the machine in short and standing down the pitch so that you're playing it as a full length, then gradually moving where you stand backwards until you're at the crease as normal and happily playing the short ball you've adjusted to.