It will be interesting to see who the other 2 headliners are. A lot of people who live locally only do 1 day of Victorious. When Mumford headlined the increase in numbers on that day was noticeable.
It may well turn out the same with KOL
(And whilst we are mentioning headliners / potential headliners playing smaller Portsmouth venues, Mumford once played The Cellars pub in Southsea (now RIP) and Pulp supported St Etienne on the pier.