I dunno what happen with small blocks (acording to the manual its not convenient to use them smaller than 2quants).

Other engines have a kind of block that produces manual PORTAL SPLITS:
A block not renderizable nor visible, but acts like PORTAL in every surface.

So, u could place it into a valley as a "cieling". If u are climbing the hill to the valley's town (with hy polycount), the town will not render untill u reach the top of the hill.
Or if u are outside of a castle's wall with a tall Keep in the highly detailed inner yard, u could place the "PORTAL" block sized to fit the inner yard an as tall as the walls. The engine should render only what u realy see, leaving the inneryard unrendered till u enter or climb ontop the outer wall.

IS ANYTHING LIKE IT IN THIS ENGINE?????