Are the placements fixed?

So I heard that the PTR placements were kinda “weird” and that would place you sometimes below of your rank or way above. Now I’ve finished the tank placements and support and I had the same results in both: 3 wins and 2 defeats. The thing is that in tank I actually got plat and in support I got gold. Is this how this is supposted to be now? Why did I got way less SR in support if I had the same results?

Your placements are based on your past history before this beta. Sort of a soft reset. The developer post from Josh Noh explains more: