nearly all speakers are all designed to be square from eachother, thats where they design the optimal sound and imaging to be at the listening location. It doesnt make sense to design a pair of speakers that need to be a certain angle, it would impossible to accurately design a stereo image with varying degrees of offset for the consumer. Its all about removing variables from the equation and one of the simplest to deal with and most important ones is the toe angle of a set of speakers (im talking about near fields here, things get much more complex with other speaker set ups)
any sort of toeing in is room dependent and usually trying to fix a speaker placement error as a stop gap.
in my own experience, I’ve played around a lot with angles and found a 90 degree (perpendicular) to really be the absolute sweet spot for imaging. The center channel for me on my set up sounds like its about 2 feet behind the speakers, behind my monitor, hitting perfectly in the center of my brain with stereo sounds dancing on the edges of my ears. Its quite the illusion tbh
in the pic i posted above, the large speakers on the flanks are only turned on when im mixing records, for volume, not imaging for production purposes
and just want to say, that what im saying here is my own experience, im certainly lacking knowledge in a lot of technical aspects here and i could be very wrong, but i think im ‘right’ in my own working knowledge in terms of a simple 2 point near field set up