4.2 Network RPC, why need to be on exactly the same node?

First I call the client and server using this code:

extends Node

func _ready():
	var args = OS.get_cmdline_args()
	if (args.size() > 1 && args[1] == 'server'):
		$Server.server_setup(13338)
	else:
		$Client.client_setup('127.0.0.1', 13338)

Then server is done like this:

extends Node

func server_setup(port):
	var custom_peer = ENetMultiplayerPeer.new()
	custom_peer.create_server(port, 4000)
	multiplayer.multiplayer_peer = custom_peer

@rpc("any_peer", "call_remote", "reliable")
func client_ready_msg():
	var charid = multiplayer.get_remote_sender_id()
	print("Connected: " + str(charid))
	pass

And client is implemented as follows:

extends Node

func client_setup(ip, port):
	var custom_peer = ENetMultiplayerPeer.new()
	custom_peer.create_client(ip, port)
	multiplayer.multiplayer_peer = custom_peer
	multiplayer.connected_to_server.connect(_on_connection_succeeded)

func _on_connection_succeeded():
	print('Sending ready...')
	await get_tree().create_timer(1).timeout
	get_node('../Server').client_ready_msg.rpc_id(1)

@rpc("any_peer", "call_remote", "reliable")
func client_ready_msg():
	print("This should not be called")
	pass

Notice the get_node('../Server').client_ready_msg.rpc_id(1) ? This is extremely ugly, do I need to put client/server logic in a node that is accessible on both client and server? Notice that I later on declared the function on the client too, but it seems it i not even needed. Has anyone got something similar working without resorting to this kind of hack?

In https://github.com/godotengine/godot/issues/57869#issuecomment-1687411210 someone got it working last year on C#, but the server won't receive the message if I try this.