CharacterMovementComponent works off of the Capsule and nothing else. If you want to use something else as the collision body for movement purposes you would need to do a custom movement component as well.
Flipbook components' collision in Characters is ignored.
1. Create a new 2D Side Scroller template project
2. Open the IdleAnimation and RunningAnimation flipbooks
3. Set the Collision Source for each to Each Frame Collision
4. In the MyCharacter BP, set the CapsuleComponent Collision Preset to Custom
5. Set all the Collision Responses to Ignore
6. Set Collision Enabled to No Collision
7. Set the Sprite component's Collision Preset to Pawn
The flipbook component's collision is ignored and the character falls through the platform below it
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