Increasing height of stand-mount -- what to expect

It depends on the speakers. Of course the general rule is to have your ears at the same height of the tweeters but with two particular speakers I have found this didn't work. My Silverline SR11s sounded much better with the tweeter raised a few inches above my ear. It was opposite with a pair of PMC DB1i speakers. The PMCs sounded best with the tweeter 4/5 inches lower. That was a bit of a shock.

Instead of raising your speakers try tilting them back. You can use a level so you know they are equal or you can use a drafting T. Place the T across the back of the speak with the long end pointed toward the listening seat. Looking down the T tilt the speakers so they are aimed at ear level. You can also use a laser aimed down the T.

I am not 100 percent sure on this, but I believe that any time you change the distance a speaker sits from a room boundry you are likely to change the tonal balance. The vast majority of the speakers I have owned sound different when moved only a couple of inches anywhere in the horizonal. I don't see how moving vertically would be any different. Note I said it sounded different and not necessarily better or worse. I like Rrog's idea of raking the speakers to get the tweeters pointed at your ears as a good place to start.

Usually speaker manuf design speakers such that the woofer distance from the floor is a specific amount. This relates to the woofer coupling to the floor for the intended bass response. Moving the speaker up chnages this distance & chnages the bass response. You might want to contact your speaker manuf to see if they have such a desired woofer-to-floor distance or not.
Yeah, sonics are not that good when your ear is above the tweeter since for most speakers the vertical dispersion is terrible (you can see this in almost every speaker tested by Stereophile). So, your idea to get your ears below the tweeter is a good one.
Usually the best sound is when your ear is 1" below the midrange driver in a 3-way & in between the drivers in a 2-way. So, it might actually be better for you to lower your seat.

Csmgolf, That is correct. Most people know the distance from the wall behind the speakers changes the tonal balance, however, there is rarely any thought given to the distance between the floor and the speaker which is a critical room boundary as well.