Alon, sorry but I can't open up your C3 project (I'm not a subscriber and the free trial is a version lower than your c3p). I just use C2.
I'll just quickly run through my setup, which is very basic.
The first thing is that I use a circle sprite as a 'mover'.
I squeeze this vertically so that it conforms to the 'perspective' of the rest of the artwork. As you can see above, the collision polygons simply follow the shape.
The properties for the pathfinder is this:
The Cell Size and Cell Border would highly depend on your own graphics and how 'tight' your moveable area is.
Note that Obstacles is set to Solids.
The next idea is that I use blocks and circles as collision and I layer them up. The best way to describe them is this picture:
The some of the highlighted blue objects represent square sprites with collision polygons shaped likewise. If you can spot also there are these flattened pink circles (with a 'C' written on it) that are circle collisions. These Sprites have the Solids behaviour attached to them, and the Pathfinder uses these to navigate around. I use a combination of these collision Sprites to make up the moveable area. (In other progs like AGS, you define the walkable area, but in C2 I define the area that should be blocked).
Here's another picture of the other scene in the demo. The pink circles are more visible here. I use a lot of them here.
My event sheet for movement is super-simple. It looks like this:
You can ignore most of it because it's mostly related to specifics of the game. As you can see it's nothing special. However, there is a 'special' workaround here that you will see in event line 35. Sometimes the player mover can get stuck because it gets too close and overlaps a collision. When it does this, Pathfinding usually fails to get a path. So what I do every time there is an attempt to walk, I check if the player mover if overlapping any of the collision Sprites (CollisionFamily). If it is overlapping, I disable Solids for the picked CollisionFamily Sprite and then regenerate the obstacle map. Then when the Pathfinding path is found, I enable the Solid again.
Hopefully that helps. I can't share the project, unfortunately, and to be honest, it is burdened with many gameplay things anyway. The pathfinding is a very simple aspect of it.