Unity and Blender don’t share the same global coordinate or scale settings. One thing you could try is using “!EXPERIMENTAL! Apply Transform” when you’re exporting an FBX. This doesn’t work for all objects you export out, but it’s used to apply the transform to what Unity would be expecting.
Rigs can be a bit finicky to work with in Unity when they have custom hierarchies or special constraints. You can also try using Empty game objects in Unity instead of Blender if it’s possible with your rig setup.