Comb filtering is another issue altogether, and the issue isn’t really applicable to stereo pairs. Comb filtering does occur with stereo pairs but it’s less noticeable because the brain isn’t processing the two inputs trying to determine what frequencies are missing. Specifically, different frequencies are missing from the input to each ear, so the other ear can fill in the blanks. 

Comb filtering occurs when there are two sources of the same information, but stereo sources do not contain exactly the same information, and our brains process the information differently. 

The information contained in the sound arriving first at the left ear and then at the right ear is compared to the information arriving first at the right ear and then at the left ear. If there is no difference between the two sets of information, the brain cannot determine location, and so the location is assumed to be center. 

If the listener is closer to one side than the other, more, if not most, elements will seem to be arriving from the nearer side. 

Comb filtering is worst, aka most noticeable, when two adjacent sources are producing identical output. In the absence of another, different or more distant source, the brain is able to recognize when frequencies drop out because they drop out dramatically, not slightly, and often they drop out from both ears. 

Back to the point, as long as the two speakers are on opposite sides of your head, and playing different (aka stereo) signals, comb filtering is not going to be a noticeable issue.  

Comb filtering becomes an issue when two speakers are playing the same signal and are at different distances from only one of your ears, aka on the same side of your head, (or one measurement  microphone.) 

The nulled frequency is more completely nulled if the difference in level is minimal, which is the case when the two speakers are very close together.  The nulled frequency is a function of the wavelength as compared to the difference in distance from one source to the other. The null will occur where one source is farther from the listener by half the wavelength of that frequency. 

The short version: Use one left speaker and one right speaker and try to fit the audience between them. 

The coverage angles are largely irrelevant in this scenario. The coverage angles and their effect on comb filtering are of greatest concern when arraying multiple speakers.