Yeah, I'd think the odds in that situation would be similar. It's quite possible it's been blown out of proportion between the theory about the possibility of an issue vs the likelihood that you could create such conditions accidentally. If it's a one in a million chance, you could grow for lifetimes and never have an issue, and I really have no idea how likely it would be to create such a situation.
You're also 100% correct on curves vs angles. same math proof as for parabolas, but you can also just think about how light reflects. An angle will reflect uniformily on either side of the angle, so you get an overlap, but much less of a concentration. smooth curves can take a great deal of diffused light and reflect that large surface area into an increasingly small focal point. If you look at different reflectors, spotlight reflectors will be smooth parabolas. Reflectors meant to give a more uniform distribution will be in the general parabola shape, but with flat surfaces inside. These reflectors are designed to spread the light more evenly over specific areas at specific heights. (side note, one of the reasons german made reflectors are the shit is because they spend the time engineering their reflectors to take advantage of all this. The same 95-99% polished spectral aluminum is used, they simply put a lot more into their design in general).