I just got my Ruger SP101 spring set from Brownells. I first put in the 9# spring. It seemed to work ok until I changed the trigger return spring that came with the kit. Then I had many misfires, so I put in the 10# spring. Same thing, still getting misfires. I then put in the 12# spring. So far the 12# is working fine, but not near the improvement that I hoped for. As flatgate said, check everything carefully before trusting it.
As to your original question, the straightest part goes toward the top.
dennie