ThickBox TB_iframe ignores height parameter.

Ok, here’s some of the link code I have to launch a ThickBox modal in the page editor window to allow a user to select shortcodes:

<a href="' . FPC_PLUGIN_URL . '/util/plugin-shortcodes.php?height=400&width=600&TB_iframe=true" class="thickbox">[shortcodes]</a>

My problem is that ThickBox completely ignores the height parameter, and I have no way to enforce the height. Is there any way of doing this? It seems like other plugins are using active calls to open ThickBox as opposed to relying on a link with the thickbox class ad that works.

Any help would be greatly appreciated!