The top plates are different with Merkur, Muhle, and Jagger razors. The Muhle razor top plate has the least curvature, so this results in more blade exposure. The Jagger top plate has slightly more curvature than Muhle, so the blade exposure is less. The Merkur top plate, from a 3 piece razor, has more curvature so there is even less blade exposure.
So although the Muhle and Jagger heads may appear identical, only the closed combed base plates are, but the top plates have slightly different curvatures. This may partly explain why the R41 open comb has an aggressive reputation because the top plate does not bend the blade quite as much as a Jagger top plate. So the R41 open comb razor could be made less aggressive by using either a Jagger top plate, or a Merkur top plate from a 3 piece razor, since they have the same threading and alignment pin positions.
One thing I have noticed is that when I placed the R41 top plate onto the closed comb plate, the 2 alignment holes were not completely full.