very interesting. I've never had an issue with heat, neither with the charging pad nor the receiver in the phone even with the thick case on. I average with mysetup between 16 to 23% charge/hr it's no 40 or 50 I get with a proper wire/adapter setup, but it's more than enough at work and totally enough while sleeping. What was your receiver rated at? the one I linked to is rated at 1000mha (whether or not it charges that fast, I can't comment, my pad is only rated at 750).
What most people don't like about these types of chargers is you can't charge while you use it, phone has to be laying on the charger and all, or they have the screen to be set constantly on or whatever which will slow down your charging. Not saying these were your issues, but I'd recommend running a few tests, it sounds like you've tried different pads, have you bought another receiver for the phone? install an app to help monitor the battery charge and usage (I find battery monitor widget fairly accurate, it'll tell you your charge your charge percentage/hr). just my thoughts for you.
But just like you said, you have to laying down the phone while it's charging, this is the biggest problem for me. In a working desk, you can still using your phone while the charging cable is connected, and the charging speed is incredibly faster then the QI charger, if you use the QI pad, you need to put it back to the pad every time, if you're busy, you don't have time to put it back and make sure they're properly aligned, that's why I eventually give up on the product.
But I just thinking, if some day in the future, the whole working desk can be a QI charger support your tablet and your phone's power, that will be a great invention for our everyday life.