Scraper, I am glad it is working for you but even to suggest that you have to find a 'sweet spot' is not good enough for me. I should just be able to plonk the phone down on the plate and not have to worry about it.
As for the Otterbox, maybe the hard shell like cases are a little better but again, I should be able to use any case, with any device and not have to worry.
I have a new Lumia 735 and have tried the official DT-601 as well as a couple of third party chargers and unless my phone is in direct contact (as in not in ANY case) connection is dodgy at best and sometimes it fails all together. Even if I spend time finding a sweet spot and making sure it is connected, the connection is intermittent and often fails.
I'd even like to think that I have a bad device but after reading multiple reviews of both various phones (including high end devices such as Samsung's S5) and of various chargers I have seen that many other people have had the same experience that I have and have just given up on Qi.
I can only feel that it is not a good start for the Qi standard and unless they get things sorted soon they will never be taken seriously.