dropdown_search with async data not looking properly

I need a dropdown which can fetch data on click i get to know dropdown_search library it solved both problems first of search items and second of get data asynchronously but i am facing problem now that its height is very large and i am shrinking it using constraint it works but, dropdown icon goes down and text go up how can i fix that.

DropdownSearch<UserModel>(
                  asyncItems: (filter) => getData(filter),
                  compareFn: (i, s) => i.isEqual(s),
                  dropdownDecoratorProps: DropDownDecoratorProps(
                    textAlignVertical: TextAlignVertical.center,
                    baseStyle: TextStyle(
                      fontSize: 12,
                    ),
                  ),
                  popupProps: PopupPropsMultiSelection.menu(
                    // isFilterOnline: true,
                    showSelectedItems: true,
                    showSearchBox: true,
                  ),
                )

Any Idea how can i fix this.