Tu.114
You're absolutely right.
Vapp is the minimum speed on approach, plus icing increment if required.
Above and beyond Vapp, company policy decides and my impression is that q400 operators tend to fall into one of two categories:
a) those that set Va (1.23vsr) as minimum clean approach speed,
b) those that set a hard speed (ex. 180/190) to cater for whatever mix of scenarios they meet in their daily operations.
Thanks for taking the time.