Consider length and width of ridge. In generally, lengthy ridges tend to be worse (and also more narrow.)

This goes hand in hand with the theory of min. phase systems which are btw free of any reflexions or resonances.
An abrupt change in FR has to cause more ringing compared to a more smooth change.

The big differences between your measurements and theory is for example that ringing at two different but very close to each other frequencies will combine into ringing at approx. the center of those frequencies. With perfectly linear devices there should be two distinct ridges all the way down.

Orthos seem to have very narrow band ringing / resonance that looks like a wall. This doesn't appear to be audible and I think it gives us hints at how tight the diaphragm is tensioned (or if it's tensioned at all.)

Seems like a null / narrow notch in the FR causing this. Could be due to the diaphragm flexing at that frequency preventing it from producing the desired sound pressure.