So the drop is seven feet, meaning the ground is three feet beneath the bottom of the four foot rail, right?
No problem. Actually, I'd call that an opportunity.
Do the safety vault at a walk, as I described earlier, and really focus on your landings. You may even want to practice rolling it out. The set-up you describe is perfect for that, and will lead to some really nice flow once you get moving a little faster.
Remember, on your rolls, that you don't want to land, THEN roll. You want to land with your body "too far" forward, more on the balls of your feet, and roll AS you land.
Good luck!