Ohhh, I see what you mean, I'm terrible at making assumptions.
24" seems pretty short, I know I've printed right up to the end of a roll after cutting it away from the tube, but never specifically started with anything shorter than 5-6' feet. I'm sure there's a hard limit where the back sensor won't let you feed any further if it doesn't sense anything. I've seen the rear take-up reel spin before when I didn't have anything attached, but I did not get that error—I think I had about 5-6' left though too.