Exactly right. Some views I've seen expressed put the 19:40 arc at the western extremity of the flight path, some have it crossing EW and some WE. The data we have doesn't distinguish one from the other but the assumption you make at that point can cause any plausible course solution to move the endpoint thousands of kms.
I have to admit defeat and hope that the investigation team have followed the right hunch. Hopefully, they do have some information which can be used to favour a particular path.