I'm not sure what the distinction is between a tarp and a tent. Andy's photo of a flat tarp + bivy is what many people think of when someone says "tarp", but what about this set-up?
This is my DIY 2-man tarp that was based on the Shires' original tarp-tent plans located here:http://www.tarptent.com/projects/tarpdesign.html
Because I'm paranoid about getting wet, I pulled out his dimensions for both my solo and 2-man around 15-20% in both length & width. In addition, because I sewed them myself with 1st quality silnylon, and spent some time practicing beforehand, all the (sealed) seams & pullouts are pretty bomber.
With the low profile, twin trekking poles, guy lines and one-side pinned to the weather side, these tarps are (hopefully) not going to collapse or cause anyone inside to get wet. (The rain peak blocks blowing side rain.) Worst case scenario, I carry a Frog Togs poncho that I can unbutton and use as yet another piece of rain protection - it's essentially a flat tarp about 1/2 the size of the one in Andy's photo upstream.
Sorry, I too am not in the habit of stepping outside in a storm just to document the effectiveness of my shelter. However, this is Whitney during a second stormy day of snow/hail - the prior afternoon I was comfortably hanging out by the Crabtree RS in the middle of lashing wind, rain, thunder & lightning: