I did some testing based on the stormy weather forecasted for our area.
Last night I made a quickie MYOG tarp from a 6x9 piece of 2mil polyethylene and pitched it over a taught ridgeline on the raised ground between 2 trees in the backyard. I had the ridgeline at about 34" above the ground, and the tarp edges staked to within 3" of the ground. This is not a super low slung pitch by any means.
On previous MYOGs with this material I used double sheet bends on the corners, which were quite secure, but that made the tarp bag out and dish. This time I made the guy attachment points with a very small tied loop of 550 cord attached with a long piece of 3M fiber-reinforced packing tape. It has held up quite well, though I am concerned that freezing weather will inactivate the adhesive. In the past I've had top quality 3M duct tape refuse to stick to polyethylene at around 30 degF. Maybe (hopefully) the difference is in attaching the tape in a warm environment first. We'll see.
Anyway, I awoke early this morning to the sound of thunder and driving rain. What a great opportunity! I went out to the tarp and the ground was dry underneath. The pitch was still tight. I threw in a CCF pad and got under the tarp, then took time to see how the mists and splash zones worked out.
- I can definitely see how the 9 foot length is pretty much the minimum I'd want for harsh rain, at least if I had no bivy. I can also see how a 7 foot width would be nice for the soloist. Unfortunately the wind was just about nil, so I couldn't test how much rain a hard wind would drive under the tarp.
- Even without the wind, I could sense the tiny mist/splash droplets creeping in at the ends, though it was very minimal. I'm sure it would be much more significant with any wind.
- It occurred to me that an unprotected down bag/quilt could be a little tricky to keep dry even with the lack of wind-driven rain, especially with condensation under a low slung tarp. It would be even harder if the hiker was already wet. This is making me lean towards a synthetic quilt.
- Not being able to sit up under a tarp simply sucks. I know, we have heroes here who camp under tiny tarps when it's 35 degF and raining buckets, all while using down gear. But I hate to think of the contortionism required for a wet hiker to get under the tarp, get situated in a down bag, keep things dry, and all while unable to sit up. It seems like it would be even more of a clusterfark for a team of 2.
So as of now I'm pretty sold on the 8x10 size, since in cuben the weight bump is very minimal and would allow 2 to use the tarp. I am still undecided on beaks. Going from a 9' long tarp to a 10' adds 6" on each end, and that adds up to a lot of buffer zone for a 6' tall person like me.
Like Bryce said, the plain rectangle offers lots of pitch options. But I must admit, again, that if a guy as analytical as Jardine sticks with beaks, there's gotta be something to that. Maybe he has decided to always go with the standard A-frame, and has chosen to give up the other pitch options.