So long as we're talking bout the existing tanks, located toward the center, I think you're correct. But if you add weight towards the ends of the trailer, regardless of how high its placed, then you really will alter the stability of the trailer. Here's a good demonstration of that...
I actually find trailer dynamics to be pretty interesting. The fact that you're towing the trailer from a hitch rather than like a fifth wheel changes the game entirely, since you've created a double pendulum. And the dynamics of a double pendulum are chaotic; so when towing, you're essentially just trying to keep everything within the tipping point of it all going haywire. Fun!
The key is in keeping the energy of the pendulum lower than the tipping point, which of course means controlling its inertia through speed, mass and distribution of mass. If you're interested, here are some good pages on trailer dynamics...
http://caravanandmotorhomebooks.com/caravan-dynamics/
https://caravanchronicles.com/guides/understanding-the-dynamics-of-towing/
It's amazing how complex it is. One of the really interesting things about a high yaw inertia is that though it's dangerous once in motion, so long as it's under control it makes the trailer feel very stable, because of course the weight actually resists sway. Once you get it going, though... That makes me a little nervous when people talk about how stable Olivers are, lol. But in truth, I think even the Legacy II is compact enough that it can't possibly have the same yaw inertia as the big boys. If I start to get nervous about it, I just look at this photo and I'm back in my happy place...