According to me, it should be 11 and this is how I have worked out as shown in the attached diagram.
However, I am not sure whether all these 11 isomers can be considered as those belonging to cyclic ether.
I had erroneously uploaded incorrect diagram earlier. Now I have uploaded the correct diagram. My specific query is whether the 11th Isomer shown in this diagram, wherein Oxygen is not part of the ring, can be considered as Cyclic Ether.