file size vs media size difference after jpg conversion

hi

i have tried converting a batch of Jpgs using both GraphicConverter and EasyBatchPhoto so that i can reduce the file size. With both applications i am getting larger file sizes than i have specified for the conversion, and also the 'get info' feature in finder and preview report different file sizes. when i open the converted images in QPict it specifies two sizes, file size (which is equivalent to finder) and Media Size (which is equivalent to Preview). When i try to embed images in Music Files it is the Media Size (Preview) which determines the increase in the music file size. But i wonder why i am getting this difference after conversion, as all of my files pre-conversion show the same file size and media size in QPict. I would like Finder to report the size that is going to count when it comes to embedding.

i hope this is clear

nick