FASA Games, Inc.

Can a player attempt to repost an attack which naturally misses?
Do players react to the information that they are being attacked or do they react to the information they have been hit?

I allow players in my game to use Riposte on an attack that misses.

I also allow the players to decide whether to attempt a defensive talent (Avoid Blow, etc) after I have told them whether they have been hit or not. I don't tell them the target number, but I do generally tell them how solid a hit it was (armor-defeating, etc).

Yes. A player can attempt a counterattack on an attack test result that misses their Physical Defense, whether using Riposte or Block and Counter.

Usually I tell the player the Game Master Character misses, do they want to counter? At 2 Strain, the answer is sometimes no. If the Game Master character hits I ask them if they want to evade? (Avoid Blow, Block and Counter, Parry, Riposte, etc.)

Keep in mind that ruling in this manner can make it tougher for your own players versus Game Master Character's that possess these talents/skills though. Since they will be able to counter your player's missed attacks as well. This makes both talents stronger. Ruling that the attack needs to hit the player's Physical Defense for the counter to trigger makes the talent weaker, but it means less Riposte/Block and Counter triggers that can slow down combat at times.