Ed,
As I'm sure you know, perceived sharpness reaches it's peak in the 5 to 10 arcminute range. For photography the classic targets are images of spilled coins or fallen leaves. Likewise with binoculars fairly informally patterned targets can vary in their perceived definition at spacial frequencies around an order lower than their effective resolution.
A few months back I reviewed the Kite Bonelli 2.0. It had an excellent effective resolution, but lacking ED glass, the CA could have been better. Indeed, in one comparison the Zeiss FL had less fringing, but the Bonellis appeared sharper. It was most easily demonstrated viewing pebbles on the shore at a distance to give an apparent 5-10' range in sizing. These were a mixture of greys and earth colours. The difference appeared reduced on other patterned targets with different colour mixes. It may have changed again as the ambient light changed as I've noted on other occasions. I don't know if this kind of response can be predicted from MTF analysis, but I suspect colour may need to be taken into consideration. I'm yet to be convinced it's an intentional part of binocular design at present but, never the less, differences appear between models and between samples of the same modlel it seems.
I must admit I've been in the habit of calling effective resolution sharpness, but here I'm referring to quite a different property. It can be quite confusing.
David