The ProJam templates have been updated in the Marketplace to fix both the Today's Featured Artist and Member, you'll want to get the code from them to fix your custom templates.
Yeah, it is hard coded in the template for the module.
You can create a jrTags_tag_cloud.tpl for your skin directory and copy the code from the modules/jrTags/templates/tag_cloud.tpl file and change the height that way.