Can anyone comment on using PCI-E risers?

I just implemented a third card on a rig using a riser - and the card in the third slot that is on the riser is only getting like 350k/H - where the other 7950 in directly in slots 1/2 are getting 550k/H.

Can riser lower hashrate that much?  Also the card with the riser won't let me set fan speed in cgminer?