I get plenty questions on how to space lures and sinkers in the spread. The diagram below is the best generic answer I can give. I fish over very compact areas of underwater terrain. Because of this I run 20' shock leaders and 3' cable leaders to keep my spread compact. After the first line I space each successive sinker and lure 2X the combined leader length further back. For my 23" combined leader length each successive line is marked 46' feet longer than the previous. Spacing sinkers and lures out like this will usually prevent tangles and adds to the illusion of schooled bait. If you're not doing a good job of spacing a sinker running too close to an adjacent lure can shut that position off.
If you run 30' shock leaders and 4' cable leaders naturally you would adjust the spacing to 34' increments. There's no reason to factor in trolling sinker cable lengths provided they're all similar it will come out in the wash. The initial 100' setback is arbitrary and depends on your fishery and how many lines you run. That can be as little as 70' or as much as 150' depending on your preference. I mark all of my lines rom where they cross the plane of the transom. For a forward rod holder you need to add length to compensate for the position on the boat.