As a Roblox developer, it is currently too hard to use sea level/replace accurately when the selection box is so large and so opaque.
This similar feature request covers my frustration pretty well:
Terrain selection boxes currently look like this for both sea level and the new “Search and Replace” tool:
Can I see what I’m doing? Not at all!
We know that you’re capable of smaller boxes. Your region tool is significantly better:
Perhaps you could make something that scales with size, such as the resize tool which looks and acts similar.
If Roblox is able to address this issue, it would improve my development experience because I would be finally be able to create detailed terrain without guessing and checking.