From what I know, ideally, the front speakers and your listening position should form a perfect triangle, ie. like what you said, equal distances on all sides. My area is less than ideal, therefore, my triangle is a bit distorted. The distance between the two fronts is a bit smaller but both fronts are equal in distance to the listening position.

Regarding angles, most important is that the fronts are pointed to your listening position. If it is in a perfect triangle position, it should be 60 degrees. If not, its smaller angles like 45-50 degrees but more importantly, pointed towards the listening position.

Additionally, if you factor in the Centre speaker, in theory, it should be equal in distance from the listening positioning as the Front speakers. Which means the three speakers is not aligned, rather, form a parabolic shape around you.

However, in reality, most people use, Audyssey ...