In theory the route for the 18:45 is Platform 8 Line 4 to SN87 Westbourne Park Line 3 to SN109 to Down Main. However since you know when, this route was barred. However, I believe it has now been reauthorised, but it seems not to be used.
As far as I can see from the train the point blades on the 8057 crossover from Line 3 to Line 2 west of SN109 have been physically removed so there is no currently no chance of the route being used.
This old post took a bit of finding, but after being out of commission since the Ladbroke Grove crash and removed entirely about three years ago, this set of points leading from Line 3 to Line 2 (protected by SN109) are now being reinstated - that is the reason for engineering works taking place in the Paddington area recently.
When commissioned again, it should lead to a slight improvement as trains can once again use Lines 4 and 3 much further from the station before being able to still access the Down Main line. There is also increased flexibility in routing
ECS▸ trains off of the Old Oak Common Flyover.