How actualy Fiora W works?

I want to know everything about that spell.It triggers me.

What i dont understand is this:

Imagine if Morgana casts Q into Fiora.Fiora does W but she directs riposte towards enemy Rengar.Will Fiora redirect CC to Rengar? Will Rengar get stuned instead of Morgana?

How does it acctualy works? What if Riven knocks Fiora from behind with her 3rd Q.Fiora uses W but she missplays(not directing W to Riven).Will she just negate the dmg,right?Riven wont be stuned,right? But either Fiora wont get knocked up?

Can Fiora block spells if she cast riposte on the oposite way where the enemy spell was casted? What happens in that scenario?(i mean does she block spells from any direction,even from behind)

I once saw Ashe ulting to baron pit.Fiora pressed W and denied Ashe ult.She wasnt even facing the direction of Ashe R. Four other members of team were near Fiora but they did not get stuned.Why arent they stuned?Fiora blocked Ashe ult for herself,but does that mean she actualy denied that stun for entire team,not just for herself????

That makes no logic...They all were grouped at single spot.Fiora actualy denied all 5 members to get stuned.I though if Sejuani/Ashe/Lissandra cast ultimate AOE spell to grouped enemies and if Fiora does W,four other members of enemy team will get stuned but FIora will not. In this scenario at baron pit NO ONE GOT STUNED.

Im confused really. Sry for bad eng.