This is true,however, I think Andy Callan is right to suggest that most battles were fought on relatively flat open moors or fields for precisely the reason that heavily armoured men did not do so well on any other terrain.
You can make terrain a feature in these battles tho.We did a demo game on a large hill, an old hill fort, and it did not take a lot of adjustment to make a good game. We recently played a battle at a ford river crossing which was also fun with a few rules prepared in advance.
Your tables look great Richard, in the posts that I have seen, and are obviously excellent for the skirmish style encounter, but you will struggle to play Billhooks on them.
Billhooks is great fun and easily the best game of any sort I have played in years so I will play it on a field , a flat field, with little terrain and keep the more pretty tables for my skirmish games.