I have pretty much the same, but if the sgminer does detect GPUs it does not matter which command you pass !
what do you get if you so sgminer -n ?
What is the -n for? (edit: I found out what it is but never tried it)
I'm still trying to find out how to control power limit and fan in the .bat file instead of after the miner starts (easy but a nuisance)
On --gpu-platform= where x can be a number from 0 to how many different types ( amd/nvidia/intel) of cards in the system including integrated graphics.
One time I had to use '0' for it to work.