Model 28% on a 5x5 grid.

1 | 5 | 9 | 13 | 17

2 | 6 | 10 | 14 | 18
3 | 7 | 11 | 15 | 19
4 | 8 | 12 | 16 | 20
0 | 0 | 7 | 14 | 28