Find Path to Location Synchronously creating weird paths


I am creating an RTS game were the movable units are non-skeletal i.e. they are only static meshes (procedural ones in fact). As there is no possibility to use the standard AI navigation like Simple Move to Location etc. with non-character actors, I found a function called Find Path to Location Synchronously. The paths are perfect when a mesh has to avoid another actor, but whenever I order a unit to move to a location and there is nothing to avoid, it follows an unnecessary curve before actually going in a straight line towards the target location.
Here are two draft images depicting the problem:

I was wondering if this could be due to the box collision mesh that is assigned to the unit. Maybe it makes a bigger “hole” in the NavMesh than the capsule components in characters, thus UE tries to construct a path avoiding a hole in the NavMesh created by the unit itself.