travolter
No. There is no way to add such values in SVP 3.1.4.
8 px means grid with 8x8 px blocksize and 0 px overlapping.
12 px means grid with 16x16 px blocksize and 4 px overlapping (1/4 of blocksize). Intermediate values of blocksize and overlapping not supported by SVP.
But we have another ways to reduce CPU load.
Please, put here your additional info (SVP - Information - Additional information) after play file with Motion vector grid: 8 px (8 pixels).