Sorry Chary,
I am only used to domestic recipes so unfortunately I cannot help you in commercial ventures.

1. This happens when you fill the tin more than half. Should be only half filled.

2. If the batter is thin, it will sink. Also you have to dust the fruit with flour before adding them. In case your recipe has a thin batter, you can sprinkle the fruit half way through the baking, in which case some will sink half way while some will stay on top.

Thanks Dharini. It is choona.

Maybe you are putting too much batter in one tin. It should not be more than half full. and decrease the temperature by one setting.

Use the same amount of cornflour and add vanilla essence.