DY – I think you are missing the point. If someone asks you if the girl is dressed tzniusdik and her knees are showing than it doesn’t matter what his standards are. She is not dress tzniyusdik. He may not mind, but that doesn’t change the halacha. If she was dressed in a way that was not tzniyus according to SOME poskim, but yes tzniyus according to others, than by all means, say so. The boys standards of tzniyus don’t determine whether or not she is dressed tzniyusly, they just determine whether or not he will APPROVE of how she dresses. If she wears pants and he doesn’t mind, then the shudduch can continue. But that doesn’t change the tzniyus answer to ‘yes’.
I think the discussion is being based on questions of hashkofa, but the example that was given was halachik.