Quench spray nozzle nose geometry - impact to reliability?

Very likely this is more due to machining or pressure retaining considerations than anything else. You'll notice the edges are chamfered, but they leave some level of flat nose at the end. This is likely to maintain material thickness minimums throughout. Small nozzles will have proportionally larger "noses" than larger nozzles due to the geometry involved.

The nozzle in your picture atomizes liquid by creating a swirling flow prior to the exit orifice. The swirl causes the fluid to form a thin film on the exit cone that atomizes as it leaves contact with the nozzle. The spray pattern is a hollow cone. A similar effect can be accomplished by spinning a cone-shaped cup at high speed to atomize fluid that gets flung-out from the lip of the cup.

Spray nozzles that have a tiny orifice with no pre-swirling of the fluid will produce a solid cone spray pattern which relies on fluid turbulence to atomize the fluid exiting the nozzle.

There are a multitude of spray nozzle designs, which operate on differing principles for differing spray patterns and fluid properties, such as particulates and clog prevention.