how to implement Jump Buffering and Control jump height

Question

I'm following Game Endeavor 2D platformer series, in his "Improve Your Game Feel With Coyote Time and Jump Buffering" tutorial I'm trying to add Jump Buffering and Let the player control the height of the jump, The problem is when player jump in mid-air it jumps to max height even when he barely press the jump key, but when it grounded he can control jump height normally

This is the whole project if you want to see it: https://github.com/yznhamzeh/my_first_platformer/tree/master/platformer_0.1

This is the player code :

extends KinematicBody2D

signal grounded_updated(is_grounded)

const UP = Vector2(0, -1)

var velocity = Vector2()
var move_speed = 100
var gravity 
var max_jump_velocity 
var min_jump_velocity
var is_grounded
var is_jumping

onready var raycasts = $RayCasts
onready var anim_player = $AnimationPlayer
onready var coyote_time = $CoyoteTimer
onready var jump_buffer = $JumpBuffer

var max_jump_height = 5.25 * 16
var min_jump_height = 2 * 16
var jump_duration = 0.5


func _ready():
    gravity = 2 * max_jump_height / pow(jump_duration, 2)
    max_jump_velocity = -sqrt(2 * gravity * max_jump_height)
    min_jump_velocity = -sqrt(2 * gravity * min_jump_height)

func _physics_process(delta):

    _apply_gravity(delta)

    var was_on_floor = is_grounded

    _get_input()

    velocity = move_and_slide(velocity, UP)

    var was_grounded = is_grounded

    is_grounded = _check_is_grounded()

    if was_grounded == null || is_grounded != was_grounded:
        emit_signal("grounded_updated", is_grounded)

    _assign_animation()

    if !is_grounded && was_on_floor && !is_jumping:
        coyote_time.start()
        velocity.y = 0
    if is_grounded && !jump_buffer.is_stopped():
        jump_buffer.stop()
        jump()





func _apply_gravity(delta):
    if coyote_time.is_stopped():
        velocity.y += gravity * delta
        if is_jumping && velocity.y >= 0:
            is_jumping = false



func _input(event):
    if event.is_action_pressed("jump") :
        if is_grounded || !coyote_time.is_stopped():
            coyote_time.stop()
            jump()
        else:
            jump_buffer.start()

    if event.is_action_released("jump") && velocity.y < min_jump_velocity:
        velocity.y = min_jump_velocity



func _get_input():
    var move_direction = -int(Input.is_action_pressed("move_left")) + int(Input.is_action_pressed("move_right"))
    velocity.x = lerp(velocity.x, move_speed * move_direction, 0.15)

    if move_direction != 0:
        $Body.scale.x = move_direction


func _get_h_weight():
    if is_grounded || !coyote_time.is_stopped():
        return 0.2
    else:
        return 1


func _check_is_grounded():
    for raycast in raycasts.get_children():
        if raycast.is_colliding():

            return true

    return false

func _assign_animation():
    var anim = "idle"

    if !is_grounded && coyote_time.is_stopped():
        anim = "jump"
    elif velocity.x > 20 or velocity.x < -20:
        anim = "run"

    if anim_player.assigned_animation != anim:
        anim_player.play(anim)

func jump():
    velocity.y = max_jump_velocity
    is_jumping = true