What's difference push stream with server script and push with flash media live encoder??

Hi

I'm multi point push streaming with adobe flash media server 4

Stream structure like this

Open Broadcaster Software (or Flash media live encoder) (RTMP) -> Home Flash media server with multi push script (main.asc)

-> Stream to 2 justintv channels + 1 dailymotion channel (1024x576 , 1750Kbps)

no problem at all when streaming to justintv

but some another stream services have speed problem

ustream can not push with this method

and dailymotion, vaughnlive push speed slow down than OBS or FMLE Direct stream

for example

when direct streaming with OBS or FMLE (Without home server) , no problem at all stream to dailymotion and vaughnlive

clearly no lag

but when push with server script, slow down push speed and unstable (it affect only for dailymotion and vaughnlive streams)

justintv upload speed same as OBS, FMLE's bitrate but dailymotion, vaughnlive bitrate always slower than justintv or OBS, FMLE

Like this - justintv , OBS, FMLE (1750Kbps~2000Kbps) but dailymotion, vaughnlive (1600Kbps~1800Kbps)

I don't understand why have push speed difference between server script push and OBS, FMLE push

Have any reason? and do not have solution???

(sorry for my bad english)