The antenna for the ST10 are inside the handle. The instructions state that you should have the ST10 either horizontal, or at the least pointing at the Q500 when flying.
The antenna inside the Q500, one is along the fuselage for flight, the Camera is inside the globe, on the back side, so you can fly out to say 1300' at 200 AGL, just barely loose video, back up to 1200, hang a 180 and loose video again. The camera is blocking it's own transmission.
Just because you loose video does not mean you have lost control of your Q, though you should cease all flight (let go of the sticks) and either hit the RTH switch, or start manually flying back towards yourself until you regain signal.
Remember, just because you flew out to 1800' at one place, or in one direction, does not mean you will get the same range at the next place you go, or even in a different direction. Lots of factors come into play, and these are not phenomenally strong transmitters we are using here.
One place I went flying, I got out to 1800 before I ran out of safe range and LOS (sill had video and RC), and waddled on back. That was about due east. I tried again going West-Northwest, and only made it out to 1300 and I lost both video and RC at the same time. Local interference, terrain...who knows.