Placement of Center Channel Speaker

Generally, you want the center channel speaker to be less then 24" higher or lower then the front mains. If has to be higher then angle it down slightly. My center channel (NHT) has a third leg you can attach to the back of the speaker that supports it when in TV's with a small top and it gives a little room to angle it yet still stay in place...if you CC doesn't have an adjustable rear leg then I suggest using blue tack (available at Audioadvisor.com) to couple the speaker to the top of the TV and whatever you are using to wedge the back of the speaker higher. I use blue tack under all my speakers to keep them from being easily knocked off the stands and isolate them from the stand.

I have my center channel on 2 Target speaker stands in front of my Samsung DLP. I've tried this same speaker before on top of a Proton monitor & the detail delivery suffered. I do use a REF 30 processor that includes speaker distance in the set-up menu, not just channel level adjustment. My center speaker is a PSB C6, my front L/R speakers are Montana SPIIs.

Everything is "balance" ultimately!...and relative to your set up, room, situation.
Placing it up high will shift the soundstage relative to mains, and will couple differently in the room, so you gotta tinker basically.
I think most would be happy this way, but depends on your desired results.
I tend to put center speakers where they best anchor the sound to the picture, and sonically SOUND THEIR BEST!...IF not the same as the left, right, and other speakers!
Your goal is to make the center sound like the mains, and vice versa. And speaker placment has a tremendous amount to do with that.
So, in short, placing the center (often compromises) where it yeilds similar(preferably "flat response") frequency response to the mains is ideal.
Also to consider is the often "chesty" sound added to the cneter when placed on top of a tv. So, tweaking and issolation often becomes necessary.
OTher consdierations are that the speaker is laying down on the TV mostly, unlike the other speakers, which changes dispersion often. So, it's a balance.
Try this...place the center speaker in your chair at "ear level" for the woofers, and play some music with bass, then walk around the front of the room/TV and see where it sounds' the best! This is a neat trick. Otherwise, sound level meter and test tones, or some sort of method to get you to get the best response from the speaker.
Aiming the speaker will effect tonality and dialog, yes.
So again, wherever ultimately the speaker sounds the best, is where it goes...assuming it flows with the rest of the soundstage, provides proper perspective and steering, and integrates to your liking. Many don't like sounds going from low to high to low agian across the front, so try.
Still, most won't care.
good luck