I think the passage about using that much terrain is more of a rule of thumb. Just my opinion though.
His example is a little extreme in the shapes used. Once 12x12 section of a city block (for example) is a lot different than 10 tiny strips that all provide cover and impede movement.
As long as both players agree to the terrain in use, seems fine to me.
EDIT: Not really a rules question, moved to GENERAL forum