Thanks to jmargaris, I solved my problem following your guide.
All changes are in one file [ Impostor_ThreeFrameBlend ]
First, use Tangent space instead of all the Local space. I modified 4 nodes:
Secondly, multiply 2 nodes by Object Scale X
the one above scaled the “display panel” (but not scaling the texture).
if only scale “display panel”, you will see this:
and the one below scaled the impostor texture itself.
then it goes correctly:
In my case, I used a [ MF_Impostor_ThreeFrameBlend ] file from Project - DreamscapeSeries, I found 3 other [ Object Scale X ] multiplied node, for reference only:
this file was verified in UE 5.2.1 and UE 5.3.1, it workd fine for Foliage / LandscapeGrassOuput / PCG Spawner usages.
Love from China.