Want to run a command when mob's health drops below a certain value

I've gotten it to work with a specific value: execute as @e[tag=ecreeper,tag=!summon_event,nbt={Health:40.0f},limit=1] at @s run say Elite Creeper Activated But if I try to make it a range it doesn't work: execute as @e[tag=ecreeper,tag=!summon_event,nbt={Health:..40.0f},limit=1] at @s run say Elite Creeper Activated