I don't know whether a smaller change means necessarily a lower probability of small blast radius, but the larger a code change is the higher the probability is of a high blast radius. Blast radius isn't necessarily going to be smaller because of change size, but the chance of it being smaller certainly does decrease in relative terms as it becomes smaller even if it never reaches zero and is still in absolute terms quite high. It's still a noticeable improvement and because of that still a worthy goal to pursue, nevermind the ancillary improvements to product/design/engineering/business coordination and delivery volume as a result of lower iteration cycle time. That's the larger win for me.