This is a guide explaining the laws that Knockback Sources utilize.
Basically, the Knockback direction is obvious when the source is in a straight line with the knockbacked champion, when the source is diagonal, it's not obvious wich direction the movement will be, from the two that could be chosen. The common rule is, the direction of the movement will always be the first direction taken counterclockwise. In case of large champions, the rule still applies.
The picture displays which direction the Voil Bomber would move, if you attacked from one of the squares or cast avalanche centered on a square. It's not completely logical so I thought I'd make a screenshot showing exactly how it works.
If you have a cyclops eye belt on your champion, and attack the Voil Bomber on the picture, it is going to move two spaces to the direction of the black arrow in the square your champion is. For example, the squares right next to the Voil Bomber naturally point straight towards it, since if you attack it with a melee champion with a Cyclops Eye Belt on, it's going to move straight away from that champion.
Also, if you cast Avalanche centered on one of the squares on the picture, the Voil Bomber is going to move to the direction of the arrow on the center square of the avalanche.
The red arrow shows the direction the Voil Bomber would move if you cast Avalanche on top of the Voil Bomber.
The white lines are there just to further show the areas in which your unit or the avalanche needs to be centered to move the Voil Bomber in a certain direction.
This image show how champions affected by a knockback source behave:.
Two example casesAugment
If any champ is to be knocked back into an object (I.E. another champ, impassible terrain such as walls, etc) it will take damage equal to 5 damage per space it is knocked back. An example would be: If you have knockback 2, and your opponent's champ is directly in contact with a wall, or another champ it will take 5 damage for each space, so KB 2 would move you two spaces ~ 5*2=10+D (D= Initial damage dealt). Remember though, you must knock back the opponent into the object, meaning you still need to follow the knockback guide to utilize this.