You are correct. They should not hang down lower than the frame rails.
What
oil pan do you have now? Change to a T
oil pan if you really need the additional
oil capacity. If you don't need the additional capacity, just use a shorter pan.
What BH are you using? If it's Lakewood or QuickTime scatterproof, you can trim off a bit on the bottom. It won't be SFI certified anymore, but you won't lose it on your driveway, either.
You could also consider welding soe heavy duty tubing to the bottom of your frame rails to act like skids over the speed bumps.