The problem with the Sinar P and F series is that the bit that attaches the camera rail to the tripod adds a few inches of elevation. I think the best solution (if you want to continue to use the Sinar) would be to find a tripod that lets one...eh, how do I say this...on some tripods, you can remove the center column and re-insert it up-side-down. This allows the camera to be very close to the ground...and takes care of that nasty "image on the ground glass is up-side-down" issue
Really, getting low is mostly a tripod issue..
As a final note, I personally think that everybody who uses a largeformat camera owes it to themselves to get a Crown or Speed Graphic in addition to what ever field or monorail camera they choose....they're just wonderfully useful cameras.