Different meshes for a multilayer

Dear all,

I have to implement in Comsol a multilayer, that has a first layer (100x100x2 [mm]) with fillets and a second layer (140x140x3 [mm]) that is a uniform parallelepiped. To mesh the second layer I should use a "mapped mesh" in combination with "swept" function. On the other hand, for the first layer I may not use the mapped mesh but a "tetrahedral mesh", due to the complex shape.

Doing these meshes, I get an error from Comsol, because when I set "swept" in the "source faces" I have to insert two faces:
1) Is the face jointed with the first layer
2) Is the remaining area of the second layer, that is (140x140) - (100x100)
The error is I must insert only one source face and only one destination face (at least in my case).

I tried to bypass this problem using the lateral faces, so 140x3 as source and 140x3 as destination, but in this case the error is that I have another domain jointed to my domain.
-> How can I resolve this problem?

I specify I am using "Form union" instead of "Form assembly". Using "Form assembly", I don't get this error, but in the simulation only one layer seems to be deformed, the second is independent, it does not deform.
-> What you suggest me to set simulating a multilayer (no friction between layers, they are jointed)?

I wish I made myself clear. Thank you in advance.

Lucio