try this
Start at atleast 1,500ft....2,000 better...The FAA test standards says you have to recover before 1,000...nothing about how high to enter, so high is good.
Pick a prominent landmark and fly towards it...lower the power down to around 15-18" mark....depends on a/c an weight, and keep altitude. This means you have to come back a bit on the cyclic...keep that vsi at 0...it shouldn't take to much input...
This will bleed off airspeed, while keeping altitude.
When you get lower than ETL, you will start to loose altitude...due to low airspeed, power and rate of descent you will know most likely enter vortex ring state...
Works for me anyway.
Timts