This is the displacement used for finite-difference-based calculations of surface area derivatives.
I know, this is a terrible way to calculate surface area derivatives -- we're working on replacing it with an analytic version. In the meantime, please use this parameter with caution. If anyone has code for a better method, please share!
The syntax is
Important: this parameter is very dependent on sdens; e.g., smaller values of dpos require larger values of sdens.