It really depends greatly on the situation that day and exactly where you are located, but 800 feet is really bad.
I fly all the time from that area. I've flown on the Philly side from Race street Pier and from Penn's Landing. I have also flown from the NJ side by Campbell field.
Now I do not have a Mavic, but if anything OcuSync is supposed to give you better signal than the LightBridge in my
Phantom 4 Pro. With my 4 Pro, I was easily able to get from the Ben Franklin, past the Battleship NJ and way past South Street.
Come to think of it I even flew my Spark from the Race Street Pier and crossed the river to get to Campbell Field. That's with only a WiFi signal. So in general you should be getting much much better that 800 feet. Maybe it was just a bad signal day. Try again and see if it is better.