After using this mod for a bit, I'm finding I can't get any nice large ore patches that I could get with other mods. I've been told about a "size multiplier" variable I can edit to get ore patches 30-40 tiles across, but I do not know how to access it or find the part to edit.

Thanks for any help.

You will need to extract the mod and edit config.lua file. There is a global_size_mult there that you can increase to increase size of all ore patches. Don't make it to big since it gets a bit buggy at higher values. 2-3 should be enough for what you want. Increasing the size will also increase amount of ore per field so you might want to reduce the global richness multiplier a bit (0.5-0.75).
To quickly test it you can run following command:
/c remote.call("RSO", "runTest", 2000, 2000)
It will discover big part of map and increase game speed to make it faster. You can take a look and see quickly what are results of your changes and then start a new game normally.