Easycaps can be built with any electrode layout. The file 10-based Electrode Layouts lists electrode layouts based on the 10%-System, including some for special investigations at the end.
If it is preferable to distribute any given number of electrodes on any desired area in a strictly equidistant fashion, this is done by triangulation.
Please find these “equidistant layouts” in the file Equidistant Layouts.
For some layouts, coordinates are available. Please inquire.