They’re not implemented to be used together. You will get unexpected results.
The weekly targets are for loose planning with just weekly goals and litle structure.
If you set out a plan and also add weekly targets, they will compound. And that’s not what you want…
It has been asked before to change this, but apparently the logic behind all this is already very complex and not easy to change. I think this will not happen until one of the devs has significant spare time, or the number of feature requests exploses.