Near field monitors in general have pretty tight sweet spots. That's an inherent trait.
The size of the sweet spot depends on the design of the speaker and especially the tweeter technology used.
As a rule of thumb horn-loaded tweeters (as your A5 has) are the most directional of all, as the tweeter response is guided or focused by a horn shaped baffle. The deeper the horn, the tighter the focus.
A lot of monitors employ such a scheme to optimize the on-axis tweeter response.
At the other end of the spectrum, ribbon or AMT tweeters offer better dispersion and a broader sweet spot.
But this none of this is set in stone. It always depends on the actual speaker design, choice of drivers, etc.
Concerning your issue with the A5's, as you can see the tweeters are horn loaded, and quite recessed into the baffle.
That is what makes them more directional than most and have a relatively narrow sweet spot.
Other similarly priced minimonitors , such as KRK g6 or ESI 05 experience, have a broader sweet spot than the A5 does, but it's not large by any means.
Probably the broadest sweet spot I've heard were from Adam Audio monitors (they use AMT tweeters).
So you might want to take a look at their most affordable model, the F5.
A footnote about speaker placement:
The most effective way to reduce directionality is by increasing the distance between the speakers and your ears.
The closer they are to you, the more directional they get and vice versa.
Edited by Bobby S - 3/11/14 at 11:04am