[DmitryOlshansky]

Rather reliability of sum is a product of reliabilty of constituents (unless redundancy was applied) where reliability is in [0,1.0] range.

[contravariant]

This is extreme nitpicking but I'd recommend seeing it as a reliability of a product of constituents.

A sum of constituents is more likely to be a situation where you're fine if at least one of the options works (e.g. a cluster with redundancy).

This will actually get you a semiring (easy to check), although whether that is really useful remains to be seen. It's nice to have anyway.