do planar or electrostatic speakers inherently

No, I have both. I do think they sound better though for other reasons at those volume levels.

Dave

I don't know about sounding "fuller", but...

Full-range electrostats tend to maintain the same tonal balance across a wide range of volume levels including very low levels, and usually have excellent detail and articulation so that you can still hear everything that's going on at low volume levels. In my opinion, full-range electrostatics are unsurpassed at low volume levels.

Planar magnetics tend to be not as good at maintaining tonal balance nor inner detail at very low volume levels.

Direct radiators may or may not do a good job with tonal balance at low volume levels; higher efficiency ones do best. Degree of detail also varies. When there's not enough, you have the urge to keep turning it up.

Note that these comments are generalizations.

Duke

In my experience, I tend to agree with your statement.

My ML Sequel IIs sounded better at moderate volumes, than they did at realistic sound levels. However, my Revel Studios sound better at realistic sound levels, than they do at moderate levels, albeit slightly.

(I think this had something to do with the speaker designs, and my not be inherent to all planer/electrostatics vs. dynamic speakers in general. The Sequel II was a little brittle at loud volumes, whereas the Studios really come to life when pushed.)

My two cents worth anyway.