Selecting an appropriate shape parameter for radial basis function mappings can be a bit tricky.
To simplify this task, you can find the script rbgShape.py in the preCICE repository.
Given the width of the mesh and the amount of vertices to cover by the support radius, this script calculates an appropriate shape parameter for Gaussian basis-functions. The script also allows to specify a custom decay.
This solves the following equation:
\[\text{shape} = \frac{\sqrt{-log(\text{decay})}}{\text{vertices} \cdot \text{meshwidth}}\]