I would just get that aluminum tape and seal up that baffle a little better and see what happens. all your trying to do is make sure the air flow is over the fins and direct it as much as possible to prevent a lot of air from going through with out coming in contact with the fins. the other thing you can do is add a small low power fan at the top vent to pull air out and increase the air flow through the area. mine has a thermostatically controlled one so as soon as the outside temp is over a certain temp it turns on, then turns off when the outside temp drops.
but get the baffles sealed up first and make sure the back baffle is the right distance from he fins or it will let to much air bypass the fins.