It's impressa type as you've noted, it could be Fino De Jete, but there are a number of popular impressa type cherimoyas around.
If you prune to create a denser canopy (opposite of what you do for prunus), you may have a higher incidence of self pollination. The key is to keep the humidity high so the female part of the flower doesn't dry out before the pollen is ready. You can spray the canopy with a hose or use foggers on a timer as well to try to increase the humidity.