Yeah, it's really 6mm... That's actually pretty common for a 500 mw 635 nm laser diode. (The beam profile is square, btw.) Dreambeamz has one just like it in his projector. Fortunately, he's using the ScanEco galvos in there, and they have larger mirrors than most other scanners so he doesn't loose quite as much power as he otherwise would. (With a set of DT-40's he'd loose half the beam as it spilled off the edge of the mirrors.)
That's the problem with high-power red diodes. The beam quality isn't nearly as good. That's the trade-off you get with high power red. (See this thread for more discussion about the problem.)
Adam