I have tested this against 1.10 to prove to myself that it isn't something I am doing incorrectly.

Commands running a radius argument from an entity in an execute command work using the radius from where the command is run, not from the most recent execute positions.

This means that in 1.10 you could kill all zombies in a 5 block radius of a villager for example.
In 1.12 the radius does not care that the execute targets the villager and instead kills all zombies in 5 blocks of the player... using exactly the same command-
e.g.
/execute @e[type=Villager] ~ ~ ~ kill @e[r=5,type=Zombie]