First in order for any reasonable speculation, we have to arrive at a reasonable date for Ramayanam. Without a consensus on the dating, it is anybody's guess. There are theories that say Lanka is somewhere in the North only, and Rama just crossed few rivers. Now we have lost under sea theories.
In my very humble opinion dating is important. Scholars have date of 3000BC to 1500BC for Mahabharatam.
According to this, Ramayanam was just around 7200BC to 5200BC (approx). Now this would/should push the dates of Mahabharatam. But that is another subject.
If we were to take these dates to be even somewhat closer, then we would have to redefine our concepts of Yugams etc. Ramayanam is supposed to have occurred in Treta Yugam. This yugam is supposed to have been around 1,300,000 years ago, right? So the calculations becomes little topsy-turvy. The only way the dating the yugam calculations can be reconciled is if we have several more yugams, and we are talking about a different Treta Yugam.
Now looking at Kumari Kandam/Lemuria time line given by R.Mathivanan, Lemuria submerged around 16,000 BC.
The oldest dating of Ramayanam is around 7200BC, so by that time there is no Kumari Kandam or Lemuria. Ramar did not have that land.
If we consider the datings of Ramayanam to be incorrect and the dating of Lemuria to be correct, then what did Rama's army cross? Kumari Kandam was connected to the present day India? So what did Hanuman and others cross? Just some rivers?
The point is any astronomical dating of Ramayanam has to reconcile with geographical dating. That is at least one of the baby steps, without which we are all like chicken without heads.