Yes, the flex is in that general vicinity. The easiest way for me to isolate the PC muscle is to stop the flow of urine while taking a piss. Really concentrate on which muscle is contracting when you do this.
Another method that might help you find it is; pull your dick straight out (while flaccid) and try to squeeze the muscle that will make your dick “flex” back towards your body. Do this 5 or 10 times and concentrate on where you feel the internal pull originating from. Once you have it, let go of your dick and flex the muscle again. That should be it.