[eno_]

Increased distance increases time between blast/shock waves and differential between the two?

Why would it? Especially if the two shocks are from the same type of source.

[CaptSkip]

Like I said I don't know the physics, but if the first blast was lower in intensity, the first blast wave might also move slower and fall of more quickly as distance increases.

The only "Law" I can speak to is the "Inverse Square Law".

"...the inverse square law applies to diverse phenomena. Point sources of gravitational force, electric field, light, sound or radiation obey the inverse square law. It is a subject of continuing debate with a source such as a skunk on top of a flag pole; will it's smell drop off according to the inverse square law?"

http://hyperphysics.phy-astr.gsu.edu/hbase/forces/isq.html