You can view the page at http://www.bushcraftuk.com/forum/content.php?r=818-DD-Hammocks-DD-Tarp-4x4-MC
I asked DD Hammocks about this very thing concerning the loops on the DD hammocks tarp M and they said:-
Regarding the loop sizes you're not really missing a technical point. They are bigger because once the tarp is pegged out (in the middle), there is often more pressure on the middle points (if they are pegged downwards, straight to the ground) and so being a little longer prevents excess stress on them (as the middle of the tarp is likely to be slightly lower than the ends of the tarp). The middle loops are still very strong but not as super strong as the side attachment points are due to the placement on the tarp and use of re-inforcement patches at the sides (that makes it sound like the middle ones are weak but they certainly aren't and we do not hear of any weaknesses/ issues with them at all). If the middle sides of the tarp are not pegged at a steep angle to the ground the loops can sit a little loose.The middle loops on all of our tarps are like this and as you mention its possible to tie a knot to make them shorter if required.
I spent years refusing to spend more than a tenner on tarps, god dammit i suffered on countless times as the wind shredded them in the middle of a storm in the middle of a night, then i bought my first dd 3X3 after my first time out with it i bought another
John I've got the 4x4 and I run a line internally to hang things from. The end ridgeline loops have a small loop on the inside of the tarp and I clip a length of bungee cord attached with mini carabiners to them. Works well as long as you use decent prussicks, otherwise it pulls the tap in a bit. I'm out with it over the weekend so I'll take a photo and post.