I haven't thoroughly tested it, but I guess the cultivation texture distribution is simply related to the number of available textures.
In other words if you have 2 textures, the distribution chances will be 50%-50%.
Now, it you have 4 textures for white houses and 1 texture for brick houses, the chances will be 4 to 1.
Technically you may set as many toc files as you want. Of course, the more you have and the longer they get, the more you load the cart...