Change bed mesh coordinates

The edges of my bed are AFU, and I only use the middle 200x200 of my 300x300 bed.

I use manual mesh bed leveling. I want to shrink my leveling mesh to basically be a 200x200 area, but I can't find where the mesh points are defined in Configuration.h.

I assume Marlin must calculate the points based on some parameters like the bed size and number of points, but I don't want to actually change my bed size I just want to shrink the mesh.

If I can't do that I guess I would settle for adding more points and just leave the outer points alone when I probe, but I'm not sure even how to add more points for sure...many of the configuration settings are targeted to bed probing, and I don't have a bed probe so I don't think I can use those, I need to figure out the options that control manual mesh leveling.

Adjust

#define X_BED_SIZE 200
#define Y_BED_SIZE 200

// Travel limits (linear=mm, rotational=°) after homing, corresponding to endstop positions.
#define X_MIN_POS -50
#define Y_MIN_POS -50
#define X_MAX_POS X_BED_SIZE
#define Y_MAX_POS Y_BED_SIZE

this will take 50mm off of all edges

I actually wanted to keep using my full bed, but just avoid the edges of the bed with the mesh. I was able to do it by changing the "mesh inset" parameter in the configuration files, I changed it from like 2mm to 50mm and it did what I was looking for.

Now that I did that, I am wondering how the firmware handles points outside the mesh, in case I ever print something out there, I assume it extrapolates somehow