I don't get the "sink to net" part at all, sorry. Do you mean that your short shots were throwing your opponents off more than the deep ones? If you're playing against a lazy opponent it can be a GREAT strategy to mix it up with short slices. They want to stand on the baseline, they're usually not expecting you to mix it up and make them move forward. Deep balls with pace on them should work though, were you struggling with power that day?