Special Shading Issue

Hi
i have an experimental project i return time to time and i cant solve one of the main issue with the lighting.
It is a 2.5D RPG and its not like "Octopath Traveller" which used 3D with 2D but still similar in some ways.
I would like to use simple one sided planes for all graphical assets.
There is the "baking" method in 3d softwares where you can put the details of a high res model on a low poly model.
So my idea was to bake high res models on simple planes and use them on a 2.5D setting.
https://mir-s3-cdn-cf.behance.net/project_modules/max_3840/df8bd561639237.5a74ac2c9048a.jpg
this is a printscreen of the editor, its an early test for the graphics both in the models and effects.

However somehow in unity all my baked planes receiving light from the opposite direction as it should be, so if the light source is up, the shadows of the "sprite" will be up too which is bad ofcourse.
So far i couldnt solve this however i tried Unreal engine with the very same assets and the light/shadows are perfectly good in that.
So its not the model's fault but actually unity's.
Can anyone solve this for me?
...
Would be awesome... i would rather stick with unity im no expert but i know this engine lightyears more than anything else...