Kangaroo - Constant Compression Shell

Hello you beautiful collective hive mind,

I am trying to model a constant compression shell (the precise name escapes me right at the minute) but essentially similar to a hanging chain model similar to feliz candela / frei otto etc. 

I started off this task thinking it would be a relatively simple operation using kangaroo to simply inflate a surface with the four outermost points as anchor / support points and using gravity (in reverse) my surface would simply inflate to a perfect form. 

The problem I am having is that my structure is flattening off at the top rather than forming a dome/spherical section. Also I would like to be able to control the stiffness to control the radius of the edges (i.e. the openings / facades once this nut has been cracked. 

If you look at my screenshot you will see the levelling off I am talking about. In terms of the stiffness of the connections - I tried to increase the stiffness of all the springs however I am worried that this is what is causing the flattening off the top. 

I tried to connect another set of springs using only the naked edges hoping this would allow me to independently control the radius of the openings while the other force objects would control the shape of the sphere (i realise that in reality only one set of forces i.e. gravity should control the  form, however my first attempts are not producing what i had hoped)

If anyone has any great ideas I'd be more than happy to receive them, I am starting to get a little stressed as time marches on and i am hoping to have some work output from this today to show tmrw! And with all things but especially GH a stressed state of mind is probably counterproductive to logically working through everything.

Many thanks to you all 

J-P