“For those that don’t know, a blue flag is shown to slower drivers to indicate them to move off the racing line for faster drivers to overtake”
IMHO, if this is why you would want to use the blue flag – don’t use it.
A slower driver should always stay on his line, but beware of faster drivers approaching, and allow those faster drivers to pass cleanly without putting up a fight. That driver should point the direction (off the racing line) they would like to be passed on.
To me, the only time a driver should move “off line” is when there’s a mechanical problem and he’s waiving his hand like his life depended on it ASAP.
Again, JMHO