@laiseran"you could see only..." would be less confusing than "you could only see..."
Here's a quote I found that should make it clearer:"At night, you could only see her eyes and teeth" would be the clearest I think.
Strictly speaking, both sentences are correct:
You can only see ten houses - could mean ten houses and nothing else
You can see only ten houses - means no more than ten houses, and whatever else there might be. The emphasis is on the number, though.