I've already got several shapes brought over from renshuu for the 3-onigiri level kanji puzzles, but I'm moving on to 1 (small) and 2 (medium) onigiri designs. I'll come up with some, no doubt, but if there's any designs you'd like to see, let me know!
smalls will be generally a 5x5 to 7x7 area, while medium can go from 7x7 to 10x10 (although it does not need to be a square). 10x10-11x11 is the current sizes for large, but a medium could easily fill that space without having as much detail.
The tricky thing is that in order for the puzzle to be reasonable ordered, no single squares (no one kanji words in the puzzle), and there should not be too many clues in the same direction next to each other.