working with flash output levels

i don't have a flash yet but i borrowed ajs SB900 witch is an amazing flash! it has a recommended subject distance guide on the main screen of the flash unit! what the subject distance guide is alls you have to do is tell it what f stop you use and than it tells you how far the subject should be away from the flash for optimal effect. i tried using 1/1 1/2, 1/4. 1/8. 1/16 and 1/32 also the subject was back lit from the sun.

all images where taken with iso 100 at 125 of a second at f 8

1/32 (under exposed)
1/16 (sort of alright)
1/8 (alright still)
1/4 (perfect!)
1/2 (getting there)

1/1 (over exposed)