I went in to have my cleats adjusted. While there, the guy who fitted me tried to tell me my 56cm Trek frame was too large (I am 5'10.5", and 56 is supposed to fit me). Here's how he "proved" his point: With my hands on the hoods, he held up a yardstick, aligned it with my fork, to show me how my upper arm (shoulder to elbow) sat several inches behind the yardstick (i.e., behind the fork). He pointed to a poster on the wall where the guy's upper arm was in line with (or slightly behind) the fork. He claimed that means my top tube is too long.

However, the guy in the poster was gripping aero bars on a tri-bike. Doesn't that move the upper body (and arm) forward? Is there any such rule of thumb that the upper arm should align with the fork...whether in the drops or on the hoods?