FMS buffer logic could modify ?

I observe FMS buffer param in Flash , if set buffer 2.0 in flash ,

but receive it from FMS buffer is show it grow up

, can't keep buffer 2 ,  it's variation 1.x  ~ 2.x , 3 ...4.......  if internet flow better , it(buffer) will grop up continued

I can't understand , it's logic how to decision this buffer params ?
Could modify it ? or has other suggest !~?

thanks !