fii data can give u a bias of their current trend but we should check/analysis 360 degree
>>check fii are net buyer/seller
>>if they long/short in index/stock future the coi will change
>>if they create speculative position they also hedge their position using option for that reason implied volatility change..
>>in this case traded value will increase but delivery % decrease
required back test because all stock have some spacial character
(example:-before sharp fall in yesbank coi change drastically and that time iv also change same way)
hope it can give you some knowledge/hint