Anything shorter than 70% of the distance from the floor to the ceiling is not a line array. It won't have the characteristics of an array and will be what is actually called a line source.

Some part of the array must couple with the floor and the ceiling. Usually this is the midrange, but it could be the woofers or the tweeters. Often its not the tweeters.

So you must spread the 7 inchers apart enough to get the 70% rule. And you will need a tweeter that goes pretty dang low in hz. Suppose the c-to-c is nine inches on the 7's. That would work for coupling, but your 7's will develop comb filter distortion at 1500hz, so you will need to find a tweeter that can cross (and pretty steeply) at below 1500hz. You will probably need a digital crossover of 48 db to do it easily(Behringer), and then you will need to bi-amp also.

It gets complicated and costly real fast.

Marlboro