Elowan This may be due to the Range setting in the build tab. What Range are you using? Normalized may be a good option if you are importing into UE. The height (tallness) of the terrain isn't always going to fit in the Terrain Definitions. It is often times lower than the default 2600m setting.
As for the math, the definitions in Gaea are really just arbitrary for the most part. All of the accurate scaling and math is done in UE and unfortunately, to avoid being an Epic Customer Service center, I don't want to mix responsibilities of who should answer scaling in UE.
Has Epic provided a response to this question before? Or a similar question?
I am more than happy to help but we should be seeing what Epic says in their documentation.
Your math looks to be accurate by just assuming what I have had to do in the past when working in UE.
Gaea also does not work with negative numbers while UE does. This makes scaling a bit tricky in UE while we know where the floor is in Gaea because it would clip the bottom and the same would be for the top, we wouldn't with UE because it would just stretch to infinity.
https://docs.unrealengine.com/5.0/en-US/landscape-technical-guide-in-unreal-engine/
^^ That document is one I referenced quite a bit on my UE projects.
When it comes to Gaea, though, I recommend playing with the different ranges in the build tab and see if they make a difference. As stated earlier, Normalized has been pretty good in the past. If you want to be technical about it, RAW is technically the most accurate but will require manual scaling which means more math.
