You're talking about what I think is one of the most challenging aspects of building a garden pond in a small yard or small space - how to make the waterfall and berm look like it's more than a pile of rocks that appeared out of nowhere. We were lucky - we started our bog/waterfall area in a raised bed portion of our yard, so the height was already naturally occurring.
j.w.'s is a beautiful example that works really, really well. I think one reason it works is that she continues the theme with her cobble path and rock walls. If that backed up to grass I'm not sure it would look as natural as it does in her setting.
You could plant the back of the berm - either right down the slope, or terrace it if that works better in your situation. You could also use a few really large boulders instead of small (or "hand") boulders - you may need help placing them, but then you could plant between the rocks and soften the whole look.
Here's a couple of examples of what I mean - on probably a much larger scale than you are talking about, but you get the idea. Neither of these are my pictures - I borrowed them directly from the Internets. And you're right - finding pictures of "waterfall butts" is not easy! People - be proud of your butts!!