It's hard for me to upload a picture, but I'll take a shot at a diagram. This is if you look at each edge, from one corner to another:
3x3:
| +|- | |
| | -|+ |
4x4:
| +|- -|+ | |
| | +|- -|+ |
5x5:
| +|- | -|+ | |
| | +|- | -|+ |
6x6:
| +|- | +|- -|+ | |
| | +|- -|+ | -|+ |
7x7:
| +|- | -|+ | +|- | |
| | +|- | -|+ | -|+ |
Does that make any sense? I've never done a 2x2, or anything bigger than a 7x7, but if you can figure out these chicken scratches you should be able to magnetize any size cube. If you'll note, a 6x6 is basically a 4x4 and a 5x5 put together.