HT and HF - we usually practise the flyaway from a normal transition, usually from 10' using about 5 degrees nose down and hover Tq plus 15%. This means the failure is given at about 40 to 50' and with around 20 kts IAS.
As soon as the failure is initiated the lever is lowered - but the Nr is allowed to decay - whilst the co pilot calls Nr, until 91% is reached and the pilot adjusts the attitude to about 2 degrees nose down (we are practising the technique for an overwater hover at 50' so there is not much height to play with). As 45 Kts is reached (usually with the aircraft between 5 and 15' agl) the lever is lowered to recover the Nr to 100% and the aircraft starts to climb. We then have a choice between continuing to accelerate to 65 kts or climb at 45 kts.
Lowering the lever to climb is counter-intuitive but it works.
When we do a single engine water take off - we advance the Nr to max (108%) and pull to droop the Nr to 91% to unstick the aircraft from the water. As soon as the aircraft is approaching SSE speed, the lever is lowered again to recover Nr as previously mentioned.
They are 2 different ways of using the rotor's energy to assist the flyaway with the first being more gradual than the second.