Let's say I'm building some woods for units to use as cover - what sort of footprint size do people use?

I'm not necessarily planning woods, but they're a classic terrain piece so I figure it helps explain the gist of the question. Depending on what seems sensible I'll figure out what my terrain actually ends up being.

I'm thinking about how many minis of different base size should fit but as I don't really play much 40K, I don't really know what works well, what's excessive, etc..

Bottom left, for example, there's a little base of "woods":

It looks like maybe five 25mm bases fit in there. That wouldn't be much good in the modern game, I suspect, as units that use 25mm bases are usually at least ten minis.