Hello!
I have a problem: the landscape at my level covers the entire leaf, which grows on trees and shrubs

applied to the landscape of multi-texturing shader (5 textures)
also "Sahde-C"

I don't understand the description of your problem.
If I can't understand, I imagine others cant either.
Please explaine with more detail...

I see it. The hill behind the tree is paradoxically covering up the leaves at the bottom of the tree as though it were in front.

I'm not entirely sure why this is happening, but I have a guess--I know there can be major sorting errors when you've accidentally applied a skin with an alpha channel to a terrain, especially with that specific shader applied. I guess it would make sense to me that this could be related to that, specifically because the alpha channel of the leaves is probably confusing the engine concerning the terrain even further. So one possible solution is to go into MED and make sure all your terrain's skins are set to 24-bit, as opposed to 32. I had a similar problem recently of seeing distant hills THROUGH near hills, and this fixed it instantly.

Ohhhh now I understand what the problem is....
Yes logan, I've run into those sorting errors too...
I think there are a number of ways to deal with that but I think it depends of how components were created...
You might try this...

Review these in the manual, there are different setting that affect their outcomes...
The values that are set, are the way I use them...
Good luck !

d3d_mipmapping = 4;
d3d_anisotropy = 7; // anisotropic filtering active Range 0 thru 7
d3d_entsort = 0; // not sorting transparent objects Range 0 thru 7
d3d_alpharef = 255; // remove overlay seams completely
d3d_alphadepth = 16; // set all TGA alpha images to 16 bit mode
d3d_autotransparency = 1; // upper left pixel color is TRANSLUCENT for all afterwards loaded textures
d3d_triplebuffer = 1;