Communion by FedEx is improper because it violates the principle of personal transmission. For example, confession to a priest over the phone is invalid, not because the priest is any less a priest when he's listening on the phone, but because electronic transmission violates the personal principle that is the key to understanding the Church's sacramental ministry.
You know that I'm being sarcastic, don't you?
I could make a strong argument that while proximity is necessary for the validity of confession and absolution it is not necessary for the validity of reception of the Eucharist.
IIRC, Bishop Sheen often told the story of a young girl who communicated herself by licking the hosts off of the floor of a desecrated church during one of the World Wars.
The priest was unavailable. She used her tongue only and returned each day till the Eucharist had been removed. She was shot on her final day and killed.
So, bishop Sheen did not seem to believe that the personal principle was the key to understanding the substantial "nature" of the Sacred Species or recieving the benefits of Holy Communion distributed recieved under unusual circumstances.
Exactly the same reason why "electronically reproduced" music is NOT EVER allowed during the Mass.