Experiences of Cycle Training

Re: signalling. I point (often at the spot in the lane where I want to go if there is a car in that lane behind me). I guess I should be "flatting" it. What's the reason behind this? More noticeable? Less likely to be confused with someone just pointing at something?

If youre accompanying that move with a look at the driver, and it works for you to let them know youre intention- then good.
the flat vs point or other hand position we use simply as at distance it works better for visibility,
your example I am guessing comes more from a situation where you are travelling simliar speeds to the traffic in adjacent lane.