i tend to move my larger sails up/forward and back for smaller sails
in the mast track that is
then i read about a formula sailor stating:
"The general rule of thumb is that the bigger the sail, the further back it is positioned on the board. Bigger sails weigh more and tend to settle the nose of the board and are often sailed with larger fins which have the same effect. Smaller sails weigh less and especially when combined with smaller fins tend to unsettle the nose of the board so moving the mast forward will counteract that trend."
is it different for formula or ???
and yes i am aware that some people just keep it @ 135 cm 
kato:
i am NOT questioning the idea of moving the mast foot
just the WHEN
do larger sails typically go forward or back on the track for you ??
Moving your mast track 1cm makes a huge difference to performance and comfort on any board.
There are basic rules, but there is nothing better than TOW and knowing your own gear.
Above is dead right: Move mast track back until board is flying on fin, then move forward slightly to settle things down.
Don't forget that boom height, mast track positions, harness line length and fins all work together. Hence the reason you need to know your own gear....
Pretty useless information really...sorry..
thank you for the "useless" information - no info is useless !!
generally my large sails are further up than back
THIS contradicts what the formula sailor was suggesting
that's all
just more useless info - i guess {sorry 
}
I can't see any reason why you would move the mast track forward or back for a bigger sail.
If the track is too far forward the board will want to keep bearing away, and if it's too far back the board will rear up on the fin. You should only have to move it small amounts at a time until it feels just right.
A couple of things that would cause you to change the mast track position would be using a weed fin (which moves the centre-of-lateral reistance further back), or adjusting the boom height.
Chris & Brett +1
I think it's a balance between board, fin and sail size, when that's right I think the mast base position will stay the same for each sail. That's what works for me any way, right or wrong. I use two sails with my favourite slalom board and have the base in the same position for both, back a little from centre of track.
i'm the same as firiebob (and i think the back half improves my early planing and accelleration), but most folk i sail with have their mast bases in the forward half of the track for almost all their various sized sails
it's a mystery
Try this ....the center of effort on a 7.5 will be different to a 5.0 so would you have the same position on the mast track. For me no,the large sail is further forward than the small sail. The C of E difference between 2 sail sizes is very small so you may not notice any board trim changes.If i ran the 7.5 at the 5.0 mast setting the fin would keep spinning out from too much back foot preasure.
A formula board behaves and drives differently to a short board so it makes sense to use the weight to control the nose.
Please note that i use a "Barn Door" very rarely and am much happier on a short board in 12kt or surfing 
joe, I have read Slowboat talking about moving his mast step back for bigger sails based on the weight argument. He knows a thing or two about trim 
