LCR speakers

What does it take for a speaker to be a true LCR? Are all MTM designs LCR or not necessarily? Let's also start listing recommended higher-end LCR models:

Avalon Studio Pro
Avalon CIT in-wall
Von Schweikert LCR-15
Dynaudio Contout T2.1 LCR

Interestingly, JM Lab Utopia Be LR differ from the center as there are no ports in the center one, so is the Coincident center. Centers may also be shielded while LR may not.
In theory, any well-designed speaker can be LCR if used as intended. That means not turning it to be horizontal if it is normally used vertically. Most MTMs, in fact, are severely compromised by placing them horizontally, regardless of what the manufacturer says. Ask yourself, why are regular high-quality speakers never (or hardly ever) horizontal?
Kr4: interesting. I suspect the diffusion pattern is substantially affected and acceptable for center use only(mostly midrange) but inadequate for frequency extremes?
as a matter of fact, a sign that I am not curious enough, I never tried my monitors horizontal. I shall, right away!
What is affected is the crossover between drivers and, of course, where that falls depends on the particular speaker. There are a few, well-designed for the purpose, center speakers but, in general, the best center is another of whatever is used for L and R. And used correctly.

Correctly as in Vertical if this is the way L and R were designed to be used?