Good Day Ronsoon, Welcome to the Forum.
Body from the BIAB Full Volume Mash IS different from 3 vessel Brewing.
It can vary a lot by the mash Temperatures, In U.s. terms 153F is a Medium body beer, 148F is a very dry Biab Brew, and 158F is a very heavy body.
Of course, the ingredients have a lot to do with the Body.
If you want to dicuss this problem with many experts about BIAB Brewing you can start a topic at
http://www.biabrewer.info/viewforum.php?f=41 "Creating Wort - Mashing, Boiling & Hopping"
Where you can talk about Ph,Temperature, Ingredients, Mash times,etc.
I hope this helps!!
Honest Officer, I swear to Drunk, I am Not God.