There is a little trick with scale and ppi.

Assuming xvi-file scale is 1:100 and ppi is something like default 72.

To place generated from photoshop raster, with default ppi 300, and map scale of 1:100 yo do not have to apply scaling on raster,

but rather specify it as a parameter to scale xvi appropriately to your raster, i.e place a command like this to .thconfig

export map -fmt xvi \

-proj plan \

-layout-scale 3 200 \

-o bottom_plan.xvi

Then your xvi will match your raster by scale.

Also I suggest using smaller in byte size raster file formats like jpeg and do not use png with transparency as background images,

because XTherion has troubles with such kind of png-s.