Your method isn't taking all the reflected impedances into account. For example, when you reflect the X2 subcircuit into the upper half, you haven't taken into account the fact that the X4 subcircuit needs to be reflected into the X2 subcircuit BEFORE you reflect the X2 subcircuit. And, in fact, BOTH the X3 and X4 subcircuits reflect their impedances into the X2 subcircuit BEFORE you reflect it into the upper half. Also, the X3 subcircuit must be reflected into X4 BEFORE you reflect the X4 subcircuit into the X2 subcircuit, which is then reflected into the top half.
And, this is just the beginning. You have to account for all these various interactions, which greatly complicate things.
I think your only hope is to solve the full circuit at once using mesh analysis, which is what I did.