Yep, with something that size, you'd need to be back around four feet.
Although natural light is better, it can be done with flash at that range, using Aperture Priority as described. Or, if the light is good enough, use AP with the camera on a tripod, no flash.
My recent builds were taken with a Nikon D80, on AP with flash. Of course, the flash can possibly 'burn out' some highlights, and can alter colour balance, but I was just to darned lazy to get the tripod out !