I've messed around with the chain line on my Expedition and 700 long enough to know what I like. The driving reason for eliminating as much tube as possible is the ease of repair. Chain repair or replacement doesn't happen often but when it does the tubes make working with the chain a bear. Once I had a chain break while on a ride, threading the chain back through the tubes while swearing at the sun beating on my head was a dirty and tedious affair. I find it easier to repair, clean and inspect the chain without the tubes in the way. Under normal sober riding conditions I never get tagged by grease.
I put a patch of tough rubber self adhering tread material on top of the crossbar to protect against chain slap. When under tension the drive chain has plenty of room.
I added a Terracycle return idler. A portion of bottom tube is necessary to guide the return chain under the crossbar. I attach the tube to the crossbar with two DiNotte large O rings and a zip tie. The other two lines seen along the crossbar are part of my electronics.
On my 700 I removed the top chain tube and left the return chain configuration unchanged.
Unlike my Expedition there is no return idler just the lower tube attached to the power idler...don't want the extra ounces of a return idler.