Tannoy Stirlings on the way!

Technically I may not be able to explain but I can say whats going on by ears. The dispersion pattern changes. To an extent it is like toeing in-out in the vertical direction. It is meant to fire straight-direct for the most coherent presentation. That thing is lost to when you tilt it. The correct presentation is achieved when speakers are standing straight and toed-in to your ears or a little in front of the ears. I have always found that to be most right sounding after trying all sorts of placements in various rooms.

Interesting.  Always go with what your ears are telling you.  They're the only measuring device that counts. 

Mine didn't start out tilted.  They started flat and pointed straight ahead.  I arrived at the tilt and toe-in over some weeks of listening and making small, gradual adjustments.  I can't say I've noticed any loss in coherence with them tilted, and I really don't have a space that makes bulky or heavy stands very convenient.  I have to temporarily move my Stirlings out of the way semi-frequently. 

Toe-in is a necessity because these are horn guided  tweeters, they quickly lose intensity as you go off axis in the horizontal direction

So, I picked up a pair of scratch-and-dent Klipsch Heresy's.  I've got them next to the Tannoys.  They've been running a few days, now, and three things are already apparent:

1. Klipsch rates the Heresy's at 99 dB efficient, and Tannoy rates the Stirlings at, I think, 92. There is not 7 dB of difference in these speakers.
2. The Tannoys eat the diminutive Klipsches in bass depth and quality.  They should beat them at depth, being a much larger cabinet.  But the Klipsches are also just much, much boomier and uncontrolled.
3. The Klipsch soundstage is not as good, but it does do a wonderful job of throwing the singer or lead instrument right out in front of the speakers.

I have a friend who owns the Heresy's. I agree with your assessment. Their impedance curve is benign however. That is why many(myself included) prefer them driven with tubes.

I also have heard other Klipsch speakers and found that their sensitivity ratings were truly overstated. That said they can be driven to play loud. Too much so for me.