Put Steve in a 1x1 hole and measure the wiggle room.  ALL the room - WiggleRoom = Steve

----------

In a 1x1 hole, I pointed the camera straight down and moved from corner to corner.  Regardless of corner or orientation, the crosshairs pointed at the farthest point of a 5x5 square from the corner.

16 = 5 + 6 + 5

That's 16 total square width, 5 for the each side of Steve, and 6 for the wiggle room.

Front/back/left/right, the closest you can get to a wall is 5.  This test is unable to confirm if Steve is 10x10 square, or a 5 radius circle.


----------

Note: this finding contradicts the original question, as Steve is 0.625 wide, and the asker was expecting more than that.  However the original question also supports this answer in the door screenshot (5 texture pixels from door).

It seems reasonable to think that Steve is an unrotating 0.625x0.625 square, which is 0.88 from corner to corner, and could not fit through the ~0.7 gap.