Probably a regular question for you:
Is the physical diameter of that circle constant or does it depend on sensor spatial res. and taking distance? I understand that taking distance is not important within reasonable limits and why that is so but I'm thinking that the diameter of the 'Nyquist circle' in actual mm would vary?
 I guess it depends on what is meant by 'pixels', original target image pixels or the captured image pixels.
The diameter of the observed/captured blur disc is set by the limiting resolution of the observer/capture device. When shot with a discrete sampling device such as an image sensor, it will be constant, a minimum of 91.67 pixels in diameter at the Nyquist frequency for a target with 144 cycles (144 / Pi x 2). The sensor resolution is limited at it's Nyquist frequency, no smaller detail then 2 pixels per cycle (= 0.5 cycles/pixel) can be reliably recorded, but detail is often reduced to zero contrast at slightly larger detail size. There may be some accidental alignment of finer detail with a single sensel, causing a local high or low, but that will produce aliasing (unless the contrast is reduced, e.g. by an AA-filter) detail will seem to grow in size which will look as a deviation in predictable patterns.
So it's the captured image pixels that will show a constant diameter limit. The printed target will exhibit (sinusoidal grating + a few 1/2/3 linewidth) features all the way down to the pixel limits of the printer (where it struggles and reveals the effects of diffusion and loss of color accuracy due to lack of sufficient ink colors for dithering).
As long as these real features are shot with a small enough magnification factor due to shooting distance (>25x focal length), those smallest features will be smaller than the Nyquist frequency can resolve. Unfortunately, the artifacts at the printing limits will be relatively easy to spot, because they became larger than the finest details, a bit similar like aliasing is larger than the finest detail, and darker due to ink diffusion. Ink diffusion will make shadow detail blend together, and the target will predict how serious it can be.