Hi Andreas,
Obvisously the sail luff curve is too shallow for the way your mast bends down low. The mast bend down low can be reduced by moving the mainsheet attachment point to the boom or clew of the sail forward, toward the mast. In doing this, a small component of mainsheet tension will travel down the boom and pull aft on the mast at the gooseneck and reduce the bend in the lower part of the mast. This will also reduce mast rotation and a mast rotation forcing system will probably be required.
The solution to your problem is a new luff curve made onto your sail. To guide your sailmaker, measure the bend characteristic of your mast. Tie the halyard to the end of the boom and sheet the mainsheet in firmly. Turn the boat over on land and support the mast at the hounds with a short ladder. Pull a tight string from the top of the mast to the gooseneck. Measure the distance from the string to the sailtrack every 50cm along the mast, top to gooseneck. This will define the correct natural bend characteristic of your mast. This curve may be too much or too little luff round for the desired overall sail camber according to your sailmaker. The sailmaker can adjust these offset measurements by multiplying them all by the same constant. For example: If the offset numbers are too large, too much mast bend, then multiply all of them by 0.8 or 0.9, whatever constant number is required to acheive the desired sail camber with this mast bend characteristic. The mast will always bend in a characteristic shape proportional to the data you took.
Bill