What amount in mm are we taking about 50 mm 80 100mm in a 12 hour period.
Not seen Hull Pot as you describe except in photos. In general, thgouh, the following is definitely true:
In common with most flooding in caves, it depends on the season and the weather during the previous few weeks as to how much rain it takes to cause catastrophic flooding anywhere. If the land is completely water-logged, it doesn't take as much as run off is almost instant and total. If it's bone dry, run-off is also almost total at first and instant.
If, on the other hand, it's Summerand there's been a bit of rain on and off for a month, then it'll take much more rain to have the same impact on a cave, as the ground will absorb lots of it and the sun will get rid of a lot of this over the next few days through evaporation.