Sivir's Ricochet is just a modified state of an auto attack that does single target damage.
Descriptions of abilities are important in the differentiation of how things get "blocked".
Yasuo: ACTIVE: Yasuo creates a gust of wind that travels forward to form a wall in front of him. The wall slowly drifts forward 50 units over 3.75 seconds, blocking all enemy projectiles with the exception of turret attacks.
Braum: Braum raises his shield in the target direction, creating a barrier that intercepts incoming non-turret enemy projectiles and reduces the damage he takes through the shield. The first instance of damage blocked by his shield is negated completely.
The problem is more with how certain instances of AOE/Damage are calculated upon braum's shield, not the ability itself.
SMD (Jinx ult) explodes on impact, so as soon as it hits something a circle of damage is created around the rocket.
Trueshot Barrage (Ezreal ult) passthrough, does damage to every enemy it passes through.
Pictures to kind of help?
Braum v Jinx SMD First damage is the AOE, but shield does not block AOE for allies.
Braum v Ezreal TB First damage is the passthrough, so the ult gets removed when hitting braum.
Hope this kind of helps to explain it for everyone that doesn't understand.