I did a small test, and the large orders appear to follow your position.

When I placed a sell order for a few thousand STEEM just below one of their large sell walls, the wall immediately moved down to stay ahead of my order, preventing it from being the best offer.

The same thing happened on the buy side. When I placed a buy order just above their large buy wall, they moved their order up to stay in front.

Based on this, it seems they only allow smaller buy and sell orders to pass while keeping control of the top of the order book.