Hi all,
I sent in a support ticket on this case, and Snapmaker confirms that there are some imperfections in the current algorithm:
Currently, linkage machining does not consider the shape of the tool. Considering the shape of the tool is a very difficult task. Currently, it is recommended to use rotation and set a relatively large margin. If it is a flat-bottomed milling cutter, it should be larger than the tool radius
I am looking forward to the point where Snapmaker will improve their algorithm - it would be a real game changer if they’d offer their linkage with correct result! Even expensive commercial software is often not offering proper XYZA machining. Go, Snapmaker, Go! 
And thanks to Support for looking into this.