I am actually the one who had his Contrail collapse on him in a rain storm.
My stake popped out of the ground.
I blame the failure as much as on the design of the stake as my inexperience with setting up my tent. (I should have put rocks or logs on top of the stakes. I now use MSR ground hog stakes with the Y shape mentioned earlier).
Anyway, I have found that the fabric does sag in the evening time due to the moisture/humidity increasing.
Henry Shire clearly states this in the instructions.
It is very easy to add tension to the Contrail. I simply using my bare hands to pull on each of the four tensioners to take up the slack before going to bed.
On the extreme side, you could use pliers on your knife (I have a leatherman squirt) to really crack up the tension, but just don't cause a seam to bust.
Having said that, I have had morning where I find that the fabric on the back end/foot end of the Contrail has sagged and could come in contact with my sleeping bag.
If it has come into contact with my bag, it just tells me that I did not put enough tension on the lines before going to bed.
I have not had any of the tensioners fail on me and loosen them up.
Regarding pitching the Contrail completely flat. If you are talking about weather protection, you can not pitch it completely flat.
The bottom perimeter of all the Tarptents has mesh to allow for ventilation to limit condensation.
There is a bathtub floor on the Contrail.
Laying the Contrail completely flat would collapse the bathtub design and allow for water to enter the tent.
Having said that, you can lower the rear struts on the back of the Contrail and velcro the rear flap from inside the tent. The sides each have an elastic loop which I have staked down to limit rain from being blown in from the sides.
The Contrail is very storm worthy.
Though my Contrail did collapse in a storm, I did not know about the appex line that can optionally be installed by the user at the front of the Contrail….just below where the pole is held in.
With that anchored down, I am sure that it would provide a lot more stability in high wind.
Hope that this helps.