One quick solution for this problem is using DynamicHeight. Set the DynamicHeight property to Yes will let the system to determine the right Height value at runtime. But this is not a perfect solution. Usually DynamicHeight will have some weird problems on the report formating if you have a complex report design.
An alternative to DynamicHeight is to calculate the Height of the ReportStringControl at your own and set the Height based on the string length of the content at run time. Use the heightOfWordWrappedString100mm() method to determine the height of words and set the Height based on this value. You could do this in the executeSection() of the SectionGroup, before the call to super().
Here is the example to do that:
public void executeSection() { ReportStringControl ctrl = this.control(fieldnum(PurchLine_1,DeliveryAddress)); ; ctrl.height100mm(ctrl.heightOfWordWrappedString100mm(PurchLine_1.DeliveryAddress)); super(); }