I am sorry Robert. I should have asked the dimensions of the 140g.
I have lately been using a Reefkeeper 2 as my aquarium controller and the beauty of this controller is in the heater and fan controls. Heaters stick on and fans are usually run only when the lights come on without an RK2. What I can do with this controller is make sure the heater only comes on when I want it as well as the fans. For the fans, I set the controller to come on at 79 and turn off at 78.5. The second set of fans are to come on at 80 and turn off at 79.5. The second set have yet to come on since the switch to LumenBrights.
You will probably be fine with the LAIII's but if you are interested in light reaching the bottom of your tank for growing clams or SPS for instance, take a look at the LumenBrights. I love 'em
My canopy is 20 inches as well and my reflectors peak out the top by two inches granted the bulb is 16" from the water and I have the large one's which are a little taller than the minis. If you have a 4ft long tank you should be fine with keeping them at 14 inches from the water to be enclosed in your canopy. Hopefully that helps.
I can't speak highly enough about the RK2 for temp control. I have made a believer out of some that could not believe I woudl not need a chiller.