Focused line arrays are not usually used in home settings.
Since I have a flat baffle line array which I have alluded to in the past, the concerns that you spoke about are completely un-noticable if they are there at all. But all the rest of the information on how to build line arrays are the same and should be followed.
You usually see focused arrays in arenas where the people aren't able to be listening in the nearfield such as a church or a stadium. In these instances, it is necessary to focus the array to keep the listeners getting the full music. If you are listening from 10 feet away you are in the near field, and the time delay issues are compensated for in your brain, if they exist at all.