Also be mindful that supplies could take even if you don’t get perk points for them. If you drop within 880 yards (1/2 Mile) of intended field, and it is in need of supplies. It will take but you will not get any perks if you don’t get the "You have landed successfully" message. Its always advisable to land (End Mission) on the concrete at any base. While you can land successfully on the grass in some cases, there are variables that can cause a ditch to occur.
Example: on the current MA map. "Fester MA" you can land on the grass in a GV within 800 yards of any type of base. Be it a Port, Vehicle Base or Air base. BUT if there are NME planes or Vehicles you may end up with a DITCH! How close you ask? Figure that one out and you win the booby prize.
Seriously though, i think about 8000 yards or closer is the threshold that determines Ditch or Successful landing.
PS i used to be able to answer every Strat question you could think of in AH. BUT a lot has changed. And we don’t have an updated help files to refer to in regards to accurate Strat system info as of yet