I would caution you not to get too overexcited about the possibility of an op-up: there are so many factors involved that unless you have inside information about specific loads you might be setting yourself up for disappointment.

Y could be overbooked leading to the removal of some J space, but then on the day there's a lot of Y no shows. Conversely the flight could be wide open for revenue but have a lot of staff waiting to standby. IRROPS might cause an a/c substitution or other pax might upgrade with miles to F at the airport.