Homes in the exclusive enclave of Belle Haven on Greenwich's shoreline are in hot demand, sending prices soaring even as other previously coveted areas throughout town, like Backcountry, fall out of favor with the wealthiest homebuyers. "The demand continues to get stronger and stronger," said Christopher Finlay, a real estate agent with Halstead Property, who last month closed a $5.2 million sale at 101 Otter Rock Drive.