RigidBody problem!

Hi, in my game the main character have to jump exactly the same distance everytime while the platform is moving forward the problem comes when i set the mass of the rigidbody = 1 the main character starts to jump on less distance with every jump and when i set it to 2 or more the character starts to jump with greater distance every jump the idea of the game is to jump exactly the same distention im pretty sure its gravity thing but im not sure how the gravity in unity works yet! I’ll appreciate every single answer on the topic THANK YOU!

UP!