Grid size and sampling
The grid controls both detail and legibility. A 4×4 sheet of sixteen large thumbnails works for a short clip where you want to see what is in each shot; a 6×8 sheet of forty-eight small ones works for a long recording where you want structure rather than detail. Even sampling across the full duration is the sensible default and is what makes the sheet a fair summary. Do not go so dense that individual thumbnails become unreadable — a sheet nobody can read is worse than a shorter video.