Here is another example of a different Nvidia card. This time in a poky little ACER Aspire case crammed (only slot) right up at the top of the case. Ambient temp is ~18C. I'm using the same SIW software in the post above. Look at the difference in temps.
On a warm day with the card doing a some work the top of the case can get too hot for my liking.
I think ambient temp, position in your case and case air flow can have a big impact. If all these parameters are good and it was my card
I'd try to return it for peace of mind if I could.