This afternoon I made some changes to my DEDA, thanks to some tips on this thread.
The plain end snap is still attached on my left, to the square MR. I found a split collar that clamps around the vertical leg to keep the Positioner at the top of the vertical leg. After the rope comes out I passed it around behind my back. The rope goes through a split ring like you use for keys which is attached to the waist of my saddle. then the rope goes to the right side. I took a delta link from one of my Ness saddles and looped it through the webbing on my Butterfly. The screw gate is on the bottom which keeps the P out at the end of the delta. The red snap is on that end of the lanyard. Red is Right.
I haven't climbed with the setup yet. After I rigged it I looped it over the tall posts on my fence and I think this is a huge improvement. If I wanted to I could add even more length to the lanyard because the loops are behind my back. Next week I'll be climbing on the setup and I'll post back.
The best place to use the DEDA is when ascending into excurrent trees or ones with a lot of limbs. This is an outgrowth of double lanyard climbing. I know that some climbers will use the end of their climbing line instead of a second lanyard but that doesn't fit my style of climbing.
The next place that the DEDA works is when the TIP keeps my climbing line at a flat angle. Then, all I count on the rope for is a descent. Less likely to use it for positioning. With the DEDA I can really fine tune my placements. When I prune I spend most of my time out in the ends of the limbs. Instead of setting up redirects, I use the lanyard for support. I still carry a small double sheave pulley for redis though.
As others have said, a long lanyard opens up a lot of different climbing and positioning situations.
The more I tweak the lanyard system the more I see how neglected this piece of kit has been in the development of technique.
Tom