First of all speakers don't " throw ". The boxes you have are 60X40 ( unless they have a different horn in them ) and will operate under the inverse square laws rules. A long throw speaker is usually described as one with a horn that allows it to maintain a high directivity. This is usually associated with narrow horns. It does not mean it throws the sound further, only that frequencies are well directed, which improves clarity over distance. A short throw box is one with a low directivity, which as you can imagine usually has a wider horn and is meant to get the sound spread out quickly. In either case they don't throw, they direct. This is only true for the horn of that speaker though. So the coverage of the box is based on the directivity of its horn. The box has no real control of frequencies outside of the horns controlled pattern. Since the box is designed to sound a certain way within that coverage, anything outside of it will not sound ideal.
Using amplitude shading ( as it seems is being done ? ) is not the best way to do it, but will work. The sound from each box will shoot through each other, but you will still have comb filtering. Obviously if a speaker is pointing in a particular direction, those directly in front of it will hear it better than the ones that are not pointed at them. I think that the goal the installers had was to try and keep coupling between boxes down by splitting their duties up. The problem is that you still have 180deg. of coverage in horizontal plane and they tried to get more coverage by splaying them in the vertical plane. So while the solution they have will work, it is not a perfect one. Ideally you would want the speakers that are meant to couple shooting towards the back of the room and the one meant to hit the front rows be a bit quieter.
In this case it's coverage vs. amplitude. Try and set it so that the level is as even in every seat as you can get it. This may mean turning a speaker up or down that you didn't think would need to be?
