Import video to flash. quality/size problems

Hello,

I’m importing video to flash and i have tested a few encode modes and i don’t see any diference between this compression profiles(i’m importing videos in MPG):

56 kbps modem (Bit Rate 34kbps)
dsl/cable 512 kbps (Bit Rate 450kbps)

I have select in both quality to 90%.
and the result are files basicly with the same size. 421k and 418k

This is supposed to be like this?
Anyone can explain me a bit better how this thing works?

Thanks in advance