I found it extremely helpful to make a dedicated zone populating character. And made him a gnome.
Then hotkeyed all of the #npcspawn commands, #kill, #heal, etc. that I'd need while populating and testing.
As long as you're the same height or shorter than what you're spawning, they won't bounce. A barbarian has a higher z coordinate than a gnome for example. So if a barbarian sized character spawned a small sized character, the small sized character would have the barbarian's z coordinate, and would constally fall to the ground over and over.
Using a gnome was pretty safe, in that I never had any bouncing NPCs. Although, you could just use the #size command on yourself to make sure you're the right size or smaller before doing any populating, but with the gnome you rarely have to worry about forgetting to resize yourself. I've only had to resize the gnome on one occasion, when I was creating these tiny tiny little spiders. I actually did a #race and #size on myself and made myself into one of these spiders and starting populating that way.
Also, just a tip for when you start on making mobs path. Mobs will bounce when they go down hills, unless you plot the points to contour the terrain. The NPCs go in a straight line, even if that line is through the air and not on the ground. The EQ client software, however, will do a bit of client side prediction and think that a mob who is in the air must be falling from somewhere. So they'll follow their path in the sky, but constantly fall all the way down to the ground then appear back in the sky again to fall all over again. So, if you create a path for an NPC that goes over a hill, you need to tailer the path about that hill so that you don't have this wierd bouncing problem.
Here's an example of what I'm talking about. The first gif is the path the NPC would follow if his path were simply the two coordinates with a hill in between. The NPC would leave the ground about half way down the hill, and start to bounce vigorously. But creating the path in such a way that it takes that hill into consideration, by adding a few more pathing points, and he looks just fine, and never leaves the ground.
http://www.geocities.com/dannglenn/path.html