Hey Pachone,
You want to keep your presentation as "natural" looking as possible.
Which means keep the roe sack as close to bottom as you can.
Trout will inhale the sack, not nibble. They dont have time to nibble on the bait, when its floating downstream.
Most times the inhale is enough to pull the float under, but sometimes the float wont go under but just slowdown/stop mid-drift.
Try not to move the bait at all during the drift. Again, natual-looking is the key. Let the river/current move the bait as it may.
Hope this helps.
*Stoty
P.S - I live in Pickering, maybe I will see you on the river one day!