Ok, test area, fragment with water. The texture is from BG2 (WTLAKE.TIS), different from the screenshot, but the problem is the same.
First I created everything in dltcep, then 'tis2ovl bb#000.wed', then in NI 'export TIS as PVRZ based'. And that's all.
(I have not yet experimented with a different background under the water texture....)
https://drive.google.com/file/d/1ko-vTia0cY8KVbTejvLYqh-ZRc1of0J7/view?usp=sharing