Paddington is complicated when it comes to interchange time, and I think I may need to make things clearer on my OSI list. Sadly you have not been overcharged because LU to EL is 20 minutes either way. The reason for this is that the EL station is like the LU station where you wait for your train within the gateline. In contrast you wait on the concourse of the NR station until your train is announced, and then go through the gates onto the correct platform.
Strangely, the additional OSIs between Lancaster Gate and Paddington EL/NR both allow 40 minutes in the Paddington direction and 20 minutes in reverse. Using the same logic as at Paddingotn the EL time ought to be 20 minutes in both directions.