Upper limit to FOF size?

I've been working on a map recently that uses several large FOFs, ranging up to approximately 10000x3000x100 fracunits in size. They have been causing strange glitches, such as appearing much smaller or larger than they are when viewed from a distance, refusing to render flats or textures, and other things. Some solid FOFs even let the player pass through at times. Is there any way to fix these problems, or are the FOFs involved simply too large for the game to handle?

EDIT: Fixed the solidity problem, but the FOFs still appear the wrong size or shape when viewed in the right way.

I guarantee you if your FOFs are 10000x3000, you need to make your map smaller.

Are you sure about that? The entire level is the area around a large airship that is constructed out of FOFs, as the player is both inside the airship and on top of it at different times. Of course, the base structure of the ship must be constructed out of large FOFs, otherwise the ship would appear ugly, with thick wings, no windows, etc. That's why the FOFs are so large.

Split them up into smaller FOFs if it helps. Still, levels constructed entirely out of FOFs usually lag immensely.

That might help. I'll try to use as few sectors as possible in the level, because as far as I know, a few large FOFs are easier to load than many small ones. Is that correct?

Also, you don't necessarily need to make the ENTIRE thing out of FOFs. Most of it can probably be in-level sectors without being ugly; it all depends on how you build it.