Well the rumor is that there are a few rules you can use, based on the game's creation matrix and in what order the game makes the levels.
1. It usually spawns within 2 spaces of a wall
2. It usually spawns 5 or more spaces away from lava and supposedly never less than 3
3. It usually spawns near a (non-quest, random) unique monster the game has placed in the level so it's usually near a group of tough foes and a boss
4. It usually spawns more than 4 squares from a door or stairwell
These are the same rules the game uses to place the Tome so odds are better than average the two will spawn near each other just based on the fact that there are only so many places either can spawn with the above rules in effect.
BUUUUUT, this is all hearsay. I have found they usually hold true but even assuming they are real rules the game uses nothing in Diablo is ever guaranteed.
I might suggest there's no need to finish the quest at any given time. You can always come back to it after you've gone deeper and come back when the enemies are a cakewalk and you can concentrate on finding the thing. Hell, see if you can collect a rare demon's brain.
I've been hoping to add Gloryhorn the Boner to my collection for a while now (he's in Andarial's area, he charges you from the small cave in the NW corner), but haven't had the time.
If that's not a thing you want to do, then there have been times I've walked down the stairs and it's right there in view so you can always just start reload spamming until you get something where it's easy to find.