First off, getting the orbat factions/units/groups to work in game has not been an issue. I've made close to 10 and they all work (so far), but I have not cracked the code on getting the preview images to display in the eden editor when hovering over a unit display name.

For moving files over from Orbat, I modified the original @testmod files and expanded the file tree so that I move my Orbat files into:

CfgFactionClasses.hpp
CfgGroups.hpp
CfgVehicles.hpp
CfgPatches.hpp
$PBOPREFIX$

My new config.cpp file is:
#include "CfgPatches.hpp"
#include "CfgFactionClasses.hpp"
#include "CfgGroups.hpp"
#include "CfgVehicles.hpp"

I use the Orbat command Export >> Full Faction (To File) + Preview Images
(For mod files I notice this really only exports the CfgVehicles.hpp information and pics to screenshots folder in profile...)

I grab the Preview images data folder from my Screenshots folder in profile and place it in the same mod export folder as the other files.

In the CfgVehicles.hpp, I have this line of code that is exported automatically, it is the 2nd line of each new class with corresponding image:
"editorPreview = \x\\addons\ofgunittest\data\preview\ofg_unit_test_medic.JPG;"

Do I need to modify this path?

For each preview .png, I use Gimp to resize each image to 455x256 and export as .jpg and replace the .png files.

I'm not sure what $PBOPREFIX$ does, but I edited it to read:
\x\\addons\ofgunittest

so it matches the exported path from the editorPreview line above.

I pack with Arma 3 Tools Addon Builder (I have done binarized and unbinarized with same results)

I add an @ to the mod parent folder and move it to my Arma Mods folder. Everything works great except no preview pic displays when hovering over class display name in Eden Editor :(

It feels like I'm missing something easy here, or that I need to change that editor preview path to something. I've unpacked a few other Orbat examples from Steam and can't seem to figure out where the error or omission is happening. Thanks all for any help!