If you are shooting spares cross-lane, you don't walk toward the middle. For example if your way of shooting the 10 is to stand as far left as you can and aim through the center arrow, you're not going to make it by walking right and sliding at the 25 board because sliding 25 and aiming 20 is going to have you shooting straight down the middle or even sending it toward the 8 pin spot! If you want to walk right then you need to aim further right than the center arrow because you wouldn't be truly shooting "cross-lane" if you're ending up near the middle.

I walk straight up and open my shoulders quite a bit to shoot the 10.

Your toes, hips, shoulders, awrswing, approach, slide, and follow through should be directed at the pins (or the target path to the pins) you are trying to hit.