Sam Martin realized after a frustrating junior year of high school basketball that it wasn’t enough to stand 6 feet, 8 inches. So the Milford resident went to work on his game during the off-season and changed schools. His effort is paying off in a big way so far this winter for the Bangor Rams. Martin has emerged as one of the top players in Class AA during his first year of competition in the big-school ranks, often battling through double-teams and even triple-teams to average more than 16 points and nine rebounds. He also anchors a defense that has allowed just 47.6 points per outing for Bangor, which was 11-3 entering Tuesday’s game at Cheverus of Portland. “He’s such a presence,” teammate Henry Westrich said.