Ebt - it's pegged out on the right corner and at the front of pic. Where it folds over the guy line at the top edge I have another point where I have attached it to the top of the pole with a carabina and a short piece of paracord. Then the open side of the flap has 3mm shock cord attached to the end, pinned out on the peg on the left of the entrance. I found the storm flap to be a tough one to figure out as you can fold a piece of material up so it fits but when you start to tension it the shape needs to change a little. Experimentation is definitely recommended and some offcuts of polythene mean you can have a few attempts to get it right before you start with your precious material
In all honesty I don't think the storm flap is going to be essential - I designed it so that you have 800mm of width behind the pole to lie down in (which is plenty wide). That gives you 1 meter of cover from the pole to the front edges of the tarp. If you set up with your back to the wind you will be dry if the wind changes direction by 90 degrees - if the wind completely changes directions and blows into the front of the tarp there still a lot of overhang to keep you dry. I considered bringing the "beak" of the entrance down lower but it is a trade off between easily getting in and out and the amount of protection you want. I like to see about a bit when I'm lying down - I'm used to having a regular tarp above me. But this design gives you a lot of cover while still giving you a good view
I didn't particularly want it to become a "tent".
Hope this makes sense,
Phil