it caught me out with the band I am with now. when I First played with them I almost came in before any one else because I was used to starting right on the down Beat and this band starts a little behind. took some getting used too I can tel l you, It has happened to others to and I have a little smile when it does Lol
To me it is easy if the beat is at the bottom of the conductors arm movement, Andre Previn (and others) have the beat at the top which is ok once you get used to it. Why introduce guesswork into it? And how else can it work when a conductor is giving an audible beat by hitting the stand?
Conductors should insist that the beat is at the bottom, like you do Shaun!
This is a simplistic view but what happens when the conductor for example slows the music on the down beat? Most of the band will be in automatic down beat mode and play ahead.
Whereas if the band is trained to play after the actual down beat has happened, they will be more in time when they 'anticipate' the actual playing beat.
Both methods have their pros and cons.
It's always a bit of a hassle when you go from one conductor to another.
I know of a musical director who beats in a large circular motion ... take your pick where the pulse in a bar is with that one!