With FrameMaker export filters, Mif2Go has to export the whole anchored frame, empty white space and all; the size of a graphic created with FrameMaker export filters is that of the anchored frame in which the graphic is displayed in FrameMaker.
For example, if you include in your document a 2" x 3" graphic enclosed in a 7" x 3" anchored frame (to center it so that there is no runaround); and if you export the graphic using a FrameMaker graphic export filter; the resulting exported graphic is 7" x 3", which is mostly whitespace.
If you are converting to HTML and the graphic in question was imported into FrameMaker by reference, you can get around this problem with the following setting:
See §31.3.1.2 Substituting graphics files for HTML for more information.