A guess tossed out earlier (perhaps too boldly):
"It’s great to want a large sweet spot, if you use
it, and if you have company that can actually appreciate it. But, understand
you are not getting the very best your system can offer. It may be the best it can
average out to over a large zone though."
Thanks ctsooner for sharing, and Richard V for minor validation:
"The only way to make the “sweet spot” larger is to lower resolution and
homogenize the signals enough to make the presentation mediocre
everywhere. RV"