RSVP CTS has tests (TC_2_X) which require 2 senders to check if IUT behaves as dictated by the spec.
In Config-1-2 IUT will act as Egress with both LSR_A and LSR_AA (connected via same STC port) used to send PATH messages.
Rest of the TC with this config(1.2) does not require the extra LSR(AA), however the LSR_AA initialization is STC controlled and turned off accordingly. The configuration for the IUT should not matter (presence of LSR AA is just an emulated Mux link by STC but should not matter from the DUT’s perspective).
The View IUT Config Info should help understand how IUT is expected to be configured for this topology.
TC_2_X might help understand from the Actions what LSR_AA is used for.