actually the "upper tricep" or long head is activated/recruited more in a stretched position...which would be overhead. overhead dbell extensions, single and 2 arm. overhead skullcrushers etc. the only variation that will still hit the long head is a tricep extension where you stand fairly far away from the pulley so you have to essentially do a pressdown and hold your arms close (to keep them from flying up)
as for reverse grip pressdowns....there is no evidence that rotating your wrist will have any influence on how the tricep contracts. the triceps extend the arm, the only influence you can have is the different angles/leverages at which you are extending the arm.