Tips on cutting the meat and ideal cook time?

I’m on my 4th batch of making beef jerky (eye round and top round) and on every batch, I cut my jerky too thick. This leads to me then overcooking(?) the meat and it being extremely chewy. I use meat scissors, and cut against the grain.

To me, my cuts look to be maybe 1/2in thick. I know 1/8 - 1/4in is recommended, but when using the scissors, I can’t seem to get any smaller without making odd shaped jerky.

I did 158° for about 5 1/2 hours today but it came out far too dry / chewy, so much so where I can’t even give this batch out to my friends.

Next time, I’m definitely going to try a sharp knife. Other than that, any other tips?