Well, if it was leaning to one side you didn't install it correctly. You have to tighten it evenly. If you have four bolts, tighten in a
1 3
4 2 pattern.
If you have two bolts, tighten them evenly. Do one turn on each bolt then go to the next, and repeat until it's tight. You want it as tight as possible without bending the card. Be careful though as it is possible to crack the video card if you over tighten it.
Also, it's only going to drop so much. There is no guarantee that it's going to drop by X amount for every situation. My card was running hot because it had a junk stock fan, so the VF900 decreased temps significantly. If your card is already running at 50*C at load then it's probably not going to cool it by much.