Yes I figured out your gear on the ground has to go directly under the hammock.
I have not tried an asym with a ridgeline. After it filled up with water I thought it was ruined and figured Asym was probably not worth it since it is so narrow on the one side.
Yes better coverage as shown.
Reason for the 13' long is I have a 12' long hammock and wanted a bit extra coverage and 13' is the perfect length to make one of these ground setups but longer. I experimented with several lengths a few years ago and 13-14' is perfect for this type of ground setup. You probably dont notice them but there are tieouts at 1.5' in on one the long side. That forms the 10' back then the corners are tucked in leaving you with a 10' x 5.5 deep x 4' high pyramid. Works better with a beak but its big