By this point, Vincent probably has this whole routine down to mostly-sleeping muscle memory. However, the person who normally sneaks into the blankets at this point is probably much more dexterous and unobtrusive than Phalanx is. And they're probably not also wrapped up in a whole other blanket that they're clumsily trying to bring with them.

Whatever his first clue might be, the person invading his sleeping space now is definitely not Robin.