At the weekend I discovered that the method I was using to put up my Hammock was fundamentally flawed, and was what was causing the sagging.
When tensioning the hammock, I was leaving the tarp connected at both ends. This meant that the tarp was taking up all the slack rather the central chord and the hammock itself, which was of course still slightly slack. As a result the tarp was being unnecessarily stretched (BAD move...), and the hammock body would simply sag when got into.
After re-tensioning with one end of the tarp not attached I found that the sag when in use was far less noticable (from 4-6 inches ground clearace to almost a foots worth), and the hammock more comfortable overall.
On the whole I think I was rather lucky not to have damaged the tarp sheet. :-?
It seems that every time I use the hammock something seems to crop up to spoil the enjoyment... on the other hand, I'm overcoming each one of them as they happen, so soon I'll get the full benefits of it!