Speaker placement and soundstage

Playing around with the toe-in will definitely alter the soundstage. The less toe-in the wider the soundstage, usually. One can also angle both speakers towards the opposite ear or beyond. Gotta experiment. After adjusting, check the center "phantom" image. Don't let a hole open up. If one does, move the speakers closer.

Also, the listening position should be at least 3 ft. from the wall behind it to avoid bass peaking. Absorbing traps behind both the speakers and the listening position will also help. First reflections must be accounted for, as mentioned by someone else.

I use more of an isosceles triangle, sitting further away than the speakers are apart.  Equilateral is not a hard rule. Toe in can vary greatly depending on room, speakers, etc. Tell us more about your current space, spacing and limitations.

No one mentioned this but for me pulling the speakers away from the from wall makes a bigger soundstage. Mine are 6 feet out. 

Per many suggestions her on Audiogon, I used the Sumiko Master Speaker Guide free at  https://www.thesoundapprentice.com/2019/11/sumiko-speaker-placement-guide.html  

along with the XLO Test & Burn-In CD available at  https://referencerecordings.com/recording/xlo-test-burn-in-cd/

I couldn't be happier with the results. 

I have found the late Jim Smith to have it correct in his exhaustive book, Get Better Sound,  that an equilateral triangle may seem neat and tidy to our brains but generally puts a distance between the speakers that is greater than optimum. A better starting point seems to be where if x is the distance from each tweeter to ear, than the distance between tweeters should be 0.83x, and begin tweaking from there.