With Shimano Z-link cables, you can't really change the straddle cable length and height. The idea with them was that you just use the Z-link and you don't have to worry about that. The thing is, the Z-link comes in several sizes and getting one that sits lower makes a huge difference.

Or you can ditch the Z-link and get a proper yoke and staddle cable. It takes a bit more thought to setup correctly but you have much better control over the result. I had a dispute with one of the senior mechanics at my LBS over this about 10 years ago. I went in looking for the shorter Z-link cables. The sales people didn't know what I was talking about so they referred me to the mechanic. He told me I needed a proper yoke and straddle cable. I left feeling miffed and bought the Z-link on the internet. Eventually I realized the mechanic was right.