When making map entities instead of level blocks, I got some distance, a lot of it. For some reason, map entities aren't clipped the same way as models, terrains, and other level geometry. They just disappear all together at once. To simulate it, make a small level with a few blocks here and there and a fairly decent open space between them (like buildings). Then make a large map entity that goes around the level (like roads). Load the map entity to the level. Add a position so that it's just near the outside edge of this test level then build the level. Run it afterwards, call up the console (pressing tab while engine is running) and type "camera.tilt=-85;". Next, do it again only with "camera.clip_far=8000;". Press the down arrow key to back up continually and watch the scenery carefully, especially the map entity. After a short while, the map entity will disappear instantly while the rest of the level geometry disappears dependent entirely on distance and gradually. Why does the map entity disappear as it does? In fact, if you were to go outside of you level just a bit and repeat this, the map entity will disappear sooner.
I'm using Windows 98SE (accessibility kit installed), Radeon 7000 series graphics card with 256 MB RAM, and A6.22 Commercial.