Help making land

Hello,

Im working on huge surs (5mil) and i think the shield bubble is killing the npc spawning. Any ideas on how to fix? the shrink wrap on my mssur export crash all the time I try, and the obj to sur makes bubbles.

edit: More clearity. What Im try to do is create land. when I make the model large enough that it looks like it horizon to horizon 20 million its kill all spawns. I make it 500000 and drop it to -500000 on the Y axis they spawn. when I try to tile the 500k the edges overlap and give flicker even know the model resizer says there all 500k it looks like there an over lap.

Thank

Jer