Dense packing would create issues but would not happen in the area you had treated for sure unless one has an unlimited donor source, it is usually for a hair line and not beyond. What would you define dense packing in terms of density, 90 FU per cm2?
Oxygen comes via the blood and sure, the denser the more blood competition but also other challenges are there in placing extremely densely apart from the fact the donor would not give enough to cover large areas, placement its self is harder. But I don't think anyone here is truly talking of dense packing as such.
If a surgeon were to place 4,000 grafts from hair line to mid-scalp, this is the norm and not dense packing, in fact the placement in a hair transplant is less dense than the patient's original density that was there, and what is in the the donor density also. So, traditionally placing at 45/40 FU per cm2 as you go back is not dense packing. Usually the frontal third of the scalp can take 3,000 grafts and 4,000 to mid-section and it takes creativity and know how to then make this look good for the patient, but it certainly is not even at the original density of pre-loss.
Most patients, unless there is scarring, will have no issue with the grafts surviving from a blood supply point of view and neo-vascularity (i.e the formation of new blood vessels) will occur to the transplanted area.
To pay as you did for 3,800 grafts is very cheap and I hope it works out.
Take care.