What image format to import is optimal for Designer ?

I see Designer support  huge list of bitmap formats but I have troubles to find a convenient one.  I prefer to keep height  in same image  alpha.  You never loses the height that way and it's easy to store and manage as RGBA since normals and roughness are totally derivative.   

But it seems only png  format is working  ok  that way and it takes forever to export from Photoshop with extra trouble of applying  alpha on a layer transparency.

Is there a good alternative ?   It seems doesn't read alphas in exr at all.    Does something weird with Tiff  like spoilng  RGB  /color  part.   PSD files work ok but  take forever to read on  Designer side  and so on. 

Does anyone know a convenient way?  I mean a file format in RGBA  style  to export from  Photoshop and import in Designer?