The eTTL calculations seem to be producing an underexposed flash by 2 stops.
I am in a small room with the flash pointed strait up an a white ceiling only 7 ft. I had one or two pop nice, but now everything seems to be underexposed. I have to set FEC to +2 in order to get an even exposure. Bouncing off this short distance shouldn't be so dark.
Actually, it should be so dark - the camera is trying to produce a mid-tone grey. You confirm that it is doing as designed by Canon. The solution is to use FEC, as you did.
Flash exposure is evaluated by the same camera gear as ambient exposure. And uses the same zones. The zoom function on a uniform wall can affect the intensity of lighting within the zones.
The camera does all the ETTL work; the Kings simply communicate the results.