hey, Heli crash sites have no "set" spawn locations, they have a few conditions,
1. no trees/forests
2. no towns/city/houses nearby (within about 200m)
3. has Open space with no cover.
4. has to be within the north 3/4 of the map.
so as you see, most of the north is open field, most of the south is forested
guess you can see the patter from the conditions.