It's up to the individual artists how they want to handle things. In general, we try to make judgment calls and be as hands-off with them as possible, so as not to pester them with every little question that comes up. Some bands are very specific about what's allowed and what's not, which ones they want under their band heading and which ones should be broken out. Steve Wynn, for example has one collection under his name for his miscellaneous solo and side projects, one collection for Dream Syndicate, and another for Gutterball. Other artist just give a blanket "go for it" as permission, and we pile everything under their name.
In most circumstances, we'd prefer that contact with the artist about questions like this go through someone who's more connected with the band, rather than coming from an LMA admin, because they don't know us from a hole in the ground.
There's really no way to have "named" sub-projects within a band's area because of how the metadata is used to render the page display - if a show is part of the YMSB collection, it'll say "Yonder Mountain String Band Live at..." in the title even if it's not strictly YMSB, because the band name is pulled from the "creator" field that's locked in when you choose the band name from the drop-down menu.