How to make COMSOL spread out mesh nodes more evenly?

Hi there,

I'm using a COMSOL model (see attached mph-file) via LiveLink in MATLAB where I especially need to reconstruct certain values throughout the whole domain (in the context of tomography/geophysics). My 3D-domain is split into two parts: one block modelling ground and one block modelling air.
Now, the problem is that COMSOL seems to generate the (free tetrahedral) mesh such that there are certain horizontally oriented layers that are "densely populated" with mesh nodes whereas other layers contain far less mesh nodes (see attached MATLAB figure). This is bad for my reconstruction where I need nodes throughout the whole domain.

Can anybody tell me how I can make COMSOL spread out the mesh nodes more evenly throughout the whole domain?

I've already played with "maximum element size" in COMSOL's mesh configuration. However, in order to get nodes into the less densely populated layers, I have to make the mesh size so small that the overall number of nodes explodes. This is not satisfactory.
Also, if I want to avoid using a "Swept mesh", because for my MATLAB reconstruction algorithm a tetrahedral mesh is better suited.

I'm grateful for any hint into the right direction.

Thanks a lot in advance,
Joerg