The Hova-Bator model with the fan is useless for incubating most herp eggs, since the fan isn't activated until temperatures around ~99 degrees, and most (if not all) herp eggs are incubated at temperatures much lower than that. Also, you have to be careful, as the fan can really be drying, interfering with the humidity levels in the incubator.
Were the leo eggs fertile? What medium did you use? How were the humidity levels? What happened (did they wrinkle, did they get moldy, did the deflate...)? 84 degrees is about the middle range for incubating leo eggs, so the temp wasn't the culprit. For more info on incubating leos, or for any other leo-related questions, check out the <a href="http://www.ssnakess.com/forums/forumdisplay.php?s=&forumid=51">Eublepharis Macularius Forum</a>