This is how Ramp Up/Down work as well as Triangle, Round and Smooth. The purpose of these Shape Types is to provide a more organic manner in how characters are affected by the Range Selectors. There is nothing to fix. This feature has been designed to behave exactly as it does.
You need to understand that the Square Shape Type only allows for a linear selection of the Text Characters, via the Range Selector (and its properties). The other Shape Types provide alternative methods to select your text. Just remember that you need to use Offset when using a Shape Type that is not Square and you will have fewer/no issues.
PathSlicer – Advanced AE Shape Layer Effect
https://www.broadcastgems.com/pathSlicer
– create highly customizable custom animated typefaces
– create amazing transitions
– create cool lower 3rds and panels
– create burst effects
Do it all on a single Shape layer with minimal keyframes.
TypeGEMs – The Most Complete Type Tool Effect for AE
https://www.broadcastgems.com/typegems/
Intensive mocha & AE Training in Singapore and Other Dangerous Locations
Adobe After Effects CC ACE/ACI
BorisFX mocha Certified Instructor