Hey i found some little errors... replace the volume part of the function with this:
Code:

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        volume = radius / 10;
	volume -= vec_dist(camera.x,vec_pos) * volume / max(0.1,radius);   //result:radius = x:volume -- ex with result = 10: 10:700=x:70
	
	trace_mode = ignore_models + ignore_passents + ignore_passable;
        if(trace(vec_pos,camera.x) != 0)   {volume /= 2;}	
 

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And tell me if it works for you