Something very interesting about the Battle of Jakku

Several months before Empire's End came out, I wrote a theory on Reddit and this is something of a follow up.
I was looking at the preview images from the upcoming On the Frontlines book and noticed something first mentioned in the TFA Visual Dictionary. Towards the end of the Battle of Jakku, the Empire fell back on the research installation located there and defended it for a time before destroying it and jumping to the Unknown Regions. At first glance, this seems completely consistent with the Observatory in *Empire's End*; however, we also know the location of the research facility from Rey's Survival Guide - Carbon Ridge. This is not the same location as the Observatory, which was built on the Plaintive Hand Plateau and is far enough away that Rax used a ship to travel from his base at Carbon Ridge to the Observatory.
It gets even more interesting; if you recall, the remaining Imperial ships fell back and defended the base for an indeterminate period of time towards the end of the battle. If you further recall, at the end of *Empire's End* Rax pushed Yupe Tashu with several Sith artifacts into the 'essence' located at the core of the planet which started a chain reaction that would destroy the planet. However, Sloane killed Rax and managed to stop the reaction, with only minutes left. Sloane then left on a replica of the Imperialis and a Sentinel droid sent out coordinates to officers considered loyal to Palpatine. Yet we also know from the VD they didn't actually leave immediately, but defended the research facility for a significant amount of time - longer than it should have taken for Jakku to be destroyed.

This series of events is puzzling. Who ordered the Empire to fall back and defend the installation? Rax was dead and Sloane left early in the battle without ever taking command. If Rax was correct that Palpatine's plan was for Jakku to be destroyed, why not just destroy the facility and leave? Why waste time defending it? Further, why not do whatever needed to be done before the battle? Why risk the Republic reaching the facility?

The most likely conclusion is Palpatine never intended the chain reaction to be completed at that time. His goal was likely for the planetary essence to be corrupted and then for the resulting chain reaction to be put on hold. Second, the messages the Sentinels dispatched probably carried more than just coordinates. They likely also carried additional instructions for their recipients. Third, there must have been something going on at the facility that required precise timing and possibly required the corruption of the essence to occur first (to mask it in the Force perhaps?). Fourth, the Emperor must have fully intended to dispense with Rax (who can no longer be relied upon to listen to the Sentinels) and use Sloane (who has no idea what's going on). Finally, the Emperor's plan extended way beyond wrecking his empire.
Suffice to say, the events of the Battle of Jakku are far more interesting than they seemed.