2.5 nm one side and you infringe controlled airspace (or at least the tolerances for your planned track). 2.5 nm the other side and you are 2.5 nm offshore at 1500 feet.
Personally, I am happy with the 1 nm column. The other thing is this is predominantly a tandem thing. It is prudent with a tandem operation to have the canopy open by 4000 feet.
A brightly coloured tandem parachute drifting down vertically is infinitely easier to see than another aircraft. Please, especially in this area, look out the window folks. Hopefully do it everywhere you are VFR.
Sunny, you have my respect on this forum but here I simply don't agree with your logic. Thankfully the regulator had enough nous to allow this operation. Obviously they are not totally against aviation.