28-50-70mm comparison of zoom power

forgive the title, not sure how to word it.

i took my 28-80mm kit lens and did a test. i set it at 28mm and stood far enough away from my patio door so that the whole door (left/right sides) were just at the left/right edges of my eyepiece while looking through my 10d.

next, i zoomed to 50mm and backed up until the door was in my field of view.

finally, i zoomed to ~70mm and backed up again until the door was in my field of view.

i paced it off heel-to-toe and it was this difference:

between 28mm and 50mm, ~7.75 feet (my feet ~11.5inches)
between 50mm and 70mm, 6 feet

so really, if one were to get a 50mm prime, one would have to move that distance forward or backward to frame pretty much anything he/she wanted to photograph. while this may not be practical in some circumstances i think it's fairly reasonable?

Remember, you were photographing a door (in Landscape mode?). The distance you need to move is proportional to the subject. If you're photographing something more than 3 ft. wide, say about 3 miles of a mountain vista, you'd have to move back about 7.75 miles to use the 50 instead of the 28. Or almost 14 miles with the 70 (and deal with the atmospherics). Zoom with your feet's only reasonable close-in.

right. i should have mentioned closer objects vs. larger, further away. thx.