Ribbons seem to have a fairly narrow vertical dispersion, which is why they are used in GROUPS in line arrays. As Rick Craig says, they have .... "lower interference patterns in the vertical plane."So if you have them facing exactly at ear level they should be great, but if you are shorter or taller of seated stature or if you stand up, the tweeter sound should go away. Do you hear anything like that?
Alternatively, you could run a line of neo domes 30 strong down the side. You'd have to cut the flanges to .9 c-to-c but this is easily done with with a jig saw. The sensitivity of this is 106 db, so electronic crossovers and bi-amplification is a better way to go than padding the tweeters.
Marlboro