Ah. This signalling stuff with lots of things to catch you out. . . Not sure where your shunt ahead signal is (I wondered if it was on the bracket signal at the junction) so this will be principle rather than specific detail.
Single lines are 'only one train at a time' 'ever' (well almost!). The 'almost' is your shunt ahead, but that is only behind a train going away into the section. No need for a limit of shunt for that because the train is going away. If the other train is coming towards through the section, then nothing moves towards it. You have to wait until it has arrived and is clear of the single line.
So, sorry, no shunting towards a train standing on the single line at the home signal.
Hope that helps, even if it's not the answer you wanted!
Paul.