What shape band?

[DecoDaze]

I'm having a diamond band made, and I'd like to wear it with an existing band. The existing band is platinum, 4mm wide, domed. Photos below (sorry about the poor quality). It has 7 sapphires evenly spaced around it (for my first son's Sept bday). The new band will be 2mm wide and have lots of tiny blue diamonds (irradiated to various shades of aqua/teal) all the way around, spaced closely together (meant to look like aquamarines for my second son's March bday). So my question is: if I want to wear these bands together, what shape should the new band have (cross-section shape). Should it be flat, or domed like the first ring? Does it matter? My jeweler says I can go either way, in terms of setting the tiny diamonds. I might wear one or both of these with other stackers as well, eventually. What would the wise people of PS do? TIA.