Place on Face tool

Normally this works pretty well, but I just received a model one of my friends printed on a Bambu printer in a specific orientation which is the most stable/easy surface to use/identify as being flat. However, the white highlighted planes somehow identified various skewed angles not at all representing the much wider, longer flat surface. I see no guidance for generating what should be the most reliable surface to identify within an STL model.

Still cannot place parts of the root part on the face. Reimporting every part you want to place on its face is pretty annoying. However the root part can be unpacked into separate objects.

Place on face is a great tool, seems that it is unavailable for parts (when you add a part to the main stl.
Is there a way to enable that?

After using the Place-On-Face tool, the bottom face, which is a perfectly flat plane, is not sliced as the first layer, but rather as 1/2 of the object, with the other half showing up in the 2nd layer. In other words, the first layer of the object is just the front half and the 2nd layer is the full object face. It still seems to print okay, but the second half, the part on layer 2, shows a rough face when finished and there is a seam where the layers overlap. Can I somehow correct the placement of the face to do the whole object face as the first slice?------------------------------------------------------------Later: The problem went away. I had to make a slight modification to the model (nothing to do with the lower face) and now the entire face is sliced properly as layer 1. I dunno...

Good to know there's a simple method instead of rotating with 3D round arrows:  Just use F on left hand menu and choose a plane.