When you have a large number of mid and a large number of tweets, you have a much greater potential for having the different lines in the array getting seriously out of balance. This is easy to compensate in a passive arrangement without even doing the measurements. Its much harder to do in an array.

My bet is that some arrays built by DIYers and even professionals have not measured the sensitivity differences and compensated accurately for them.

My line array has a mid sensitivity of 95 and a tweeter sensitivity of 106. Even without looking at the frequency response and db's my tweeters will tend to be more forward.

Secondly, being in the near field will tend to make you feel more like you are in the middle of things. The nature of the beast is such that the midrange on an array will probably feel more intense.

Thirdly, with point source speakers only one or two speakers are handling the entire midrange. As the volume goes up so does the distortion, and the detail is lost. With Line arrays so many more speakers are handling the midrange(in my case actually 34 of them) that the detail is not lost as the volume goes up. This detail at high volumes is often mistaken for "forwardness".

Hope this helps. It may stuff you already know.

Hopefully others will step in and answer your question also