Layer and natural

I sometimes map underground caves. I map paths with highway=path and layer=-1 and everything works fine.
But sometimes there is no path and just a big underground area. I map the area with natural=bare_rock and layer=-1.
Unfortunately, the osm website does not understand this notation and draws the rock above the open air surface (grass, trees, etc) instead that below, just because the underground area is smaller.
Am I drawing it wrong? Is the osm renderer wrong?

You are aware of this wiki pages

Cave - OpenStreetMap Wiki

Proposal:Natural=cave - OpenStreetMap Wiki

dealing with your issue? natural=bare_rock does not describe the cave but the material surrouding the cave so this is not a good tagging approach imho.