Hello,
Here's simple modification of GLOBALS.DAT file to eliminate monsters and NPCs fading.
Played few hours, didn't notice any side-effects or weird behaviour, so if you're annoyed by monsters appearing too late, give it a try.
Edit: I've tweaked values a bit. I did it by having NPC placed right in the screen's top right corner ("farthest" point in isometric view) and watching when he dissapears.
I managed to reduce active range by 15% without fading. I've read that some of you have aggro issues so this is the minimum distance I can set.
PAK file (no injections needed thanks to fgaaghf's great tool)