l3DT limit import

I’ve been playing with the L3DT (Pro Trial Version) and ran into a curious thing. The smallest size (256x256) worked after I imported it into NWN2 with YATT. I then made a bigger map (1024x1024), cut it into smaller sizes (256x256) and it worked. I then went for a 2048x2048 map and cut it into smaller sizes (256x256) but when I imported into YATT . . . the topography washed into a almost flat plain . . . meaning no definition at all. My guess is that the L3DT program doesn’t maintain the heightfield map definition too well as it gets bigger. Has anyone else run into this?