The oddity of these microphones is that unlike most others, the tiny rectangular gold colored sealed-back capsule with an array of 12 entry holes open on only one side of it is actually positioned sideways inside the body & grid housing. But when either grid is installed, the opening to the outside world through which sound enters the microphone is fully straight on (the microphone is end-addressed). When used as intended with one of the two supplied grids installed, the microphone is truly omnidirectional (meaning orientation of the microphone makes no difference in terns of it's pattern sensitivity) up to just below the highest audible frequency range. Above that it becomes slightly directional at very high frequencies as would be expected of any end-address single-diaphragm omni, the difference being the very small diameter of the microphone shifts that transition up an additional 6 or 7 kHz beyond where it tends to occur in a small diaphragm pencil microphones that typically have a diameter of something like 0.75 to 1 inch.
Without any grid installed (which is not an intended use configuration as designed), the rectangular capsule housing extends party out beyond the body of the microphone. That will make it partly side-addressed, yet that aspect only becomes significant in terms of polar response at very high frequencies above about 12kHz, due to the small dimensions of the rectangular capsule.
When comparing the standard version of the microphone that uses a brass body, and the newer heavy-duty option version which uses a stainless steel body along with a larger diameter cable, how much the capsule extends past the body of the microphone appears to differ slightly. Without a grid in place on the standard version, about half the array of 12 holes extends beyond the edge of the brass tube (see the image shown on the response graph in the first post). In the heavy-duty version it appears that more of the capsule extends past the end of the machined stainless-steel body, exposing an additional row of 3 holes (as pictured in audBall's post above). I have to imagine DPA designed the grids of the heavy duty version so that it provides a response identical to that of the standard version of the microphone. We don't have a measurement of the heavy-duty version without a grid installed, but my speculation is that because the enclosed portion of the body into which the capsule it fitted is more shallow and thus the volume it encloses less, the Helmholtz resonance imparted by that volume will be less significant and higher still in frequency, making the response up around 12kHz flatter than the standard version without any grid.. yet with a similar very high frequency transition to side-address-ish'ness.
So.. folks who want to use these without any grid for flattest possible response might want to choose the heavy-duty version over the standard version.
I'd like to see what the even smaller DPA 6060 omni looks like without its grid installed.. if the grid is removable at all, it may not be.