If I understand correctly, you are talking about never going outside the edge of the center speaker, correct? Just thinking out loud, if the left and right speakers have a narrow horizontal dispersion, then your tight measurement pattern could be placing the mic outside of the dispersion of the two speakers. To compensate for what Audyssey is seeing as a drop-off of the high frequencies, it may be applying a boost, which may be why it sounds so bright.
If you are going to recalibrate anyway, you might consider a measurement pattern that places the spots on the left and right of the MLP further out so that the mic is even with the tweeters on the left and right speakers. It may be worth a try.
Edit: I believe you said the speakers are angled upwards. In addition, are the left and right speakers pointing to the MLP? If not, this is something else you might try. Many of us aim our left and right speakers so they point directly at the MLP.