Add runway to test map for testing slope entry at max velocity. Raise ground plane horizontality to a configurable exponent before using it to modulate forward acceleration. Experimentally, 1.0 (equivalent to not doing this) is too strict, and the strictest value which is lenient enough seems to be 0.45.

characters/base/character.gd

@@ -77,6 +77,15 @@ class_name Character extends RigidBody3D
 ## then that contact surface is considered a wall or ceiling;
 ## otherwise, it is ground, and can be walked upon.
 @export var _max_slope_angle: float = 1.0
+## Forward acceleration is modulated by the absolute dot product
+## of the ground plane with Vector3.UP, or in other words,
+## by the extent to which the ground plane is horizontal.
+## This helps prevent unrealistic slope-climbing.
+## Before modulation, the absolute dot product is raised
+## to the power of the value given here.
+## The closer this value is to 0, the easier it will be
+## for the character to climb slopes, and vice versa.
+@export var _accel_mod_strictness: float = 0.45
 ## Friction when standing still.
 ## [br][br]
 ## Friction at or above top speed is always 0.0.
@@ -616,7 +625,7 @@ func _do_standard_motion(delta: float) -> void:
 					# modulate it by the horizontality of the ground plane.
 					# This helps prevent unrealistic climbing.
 					_ground_acceleration *
-					abs(ground_normal.dot(Vector3.UP))
+					(abs(ground_normal.dot(Vector3.UP))**_accel_mod_strictness)
 				)
 			)
 			# Then, calculate true forward acceleration as follows: