hello there!
the 70D has an issue with using a flash gun and bouncing it, straight on its ok, otherwise its a dark image, using FEL can sort it, but its not the best option, lot of users saying the 70D behaves in a different manor to say the 6D or any other canon
more here http://photography-on-the.net/forum/showthread.php?t=1442842&page=1
i have a 350D and using a flash gun bounced, it pretty much is a good image, same method on the 70D, same settings and lens, and gun , its darker, again FEL does fix it, but have to use it every time!
is it possible to compare the firmware from a 70D and a 6D or any other canon?
my feeling is ( and its just a thought) its as if the camera and flash on bounce , refuses to increase power on bounce, bearing in mind, the pre-flash should tell the camera, the power level needed?