As promised, reporting back about my experiment with cooling by adding a small air gap between the plastic bottom plate and the metal bottom plate; which acts as a heatsink for the unit. Well, after letting it sit running overnight with air gap and horizontally right side up, the metal plate measured between 47-50C. So, not as good as flipping the thing upside down, but certainly a noticeable improvement over the usual 54-55C. If your ambient is warm, these methods could be a way to add a little extra margin.
next up, I have it sitting vertically right now and will measure tomorrow to see how well that orientation cools. I'm leaving the air gap in-place as I think that will be more effective for the vertical configuration anyway. To be honest, looking at the design of the plastic bottom plate, it doesn't appear to allow much air flow over the metal heatsink. In fact, it almost seems like it creates chambers of static air between the plastic and metal, which in effective becomes an insulator.
in the end, I feel a bit uncomfortable with the amount of heat this thing generates, even though the kill-a-watt says the Tablo 4-tuner only consumes about 10-11 watts and I know Tablo has stated 55C is normal. I may try the laptop cooling USB fan idea too and take some measurements to see how effective that is and how much extra power it will consume.