If you need a climbable with a custom height you can always create it using the ClimbableLadder or ClimbableObstacle prefab as a starting point.

When setting up a custom climbable it is important that the pivot point remains at the lower point of the visuals. Also, the object ExitBottom is recommended to stay at Y=0

To adjust a climbable’s height, adjust the visuals by removing pieces from the top (except the finalpiece with the bending handrail) and move the ExitTop point accordingly to be positioned at ground level.

Finally, adjust the collider so it always extends slightly above the ExitTop object.

If your climbable requires a specific animation or different traversing parameters (speed or positioning). You will need to create a custom ClimbableSetup file and assign it on the Climbable component. Check how to setup a custom climbing animation for more information on the topic.