Way back when I first started out I had a HH for a little while and was having the same problem. The consensus is that the tarp hooked to the hammock suspension flat out sucks. You can pull and pull as much as you want to get it tight...right up to the point of hopping in the hammock where your body weight will change the angle of the suspension and almost guarantee the tarp will sag down on you and the hammock. Getting a bigger tarp will only increase the problem. String you tarp separate from the hammock to keep it tight no matter what your hammocks suspension is doing.
here is a throw back a few years to that thread. LINK