I placed a castle on a test shard once, but I knew that the area in question had castles on Atlantic. It's still very tricky unless you have the knack. Could be a little bird blocking you... and you can't see a wide enough area to know it's clear. Even with smaller houses, I always use a single reg to help mark the walls. All you can really do is try and try and try again. If something’s blocking, I wouldn’t think staff would be willing to help. It would be nice... but a daydream, I hate to say.
You could always try the help page, but good luck.