ng-options上的popover隐藏在ng-options容器后面

Question

在某些情况下，当我将鼠标悬停在ng-options上时，我需要在它们上显示popover或工具提示，当前显示在ng-select容器的后面。使用z-index和positions：相对/绝对也无济于事。下面是当前UI视图的代码段和快照

和代码快照如下

<ng-select [items]="instanceList"
                             #temp
                             bindLabel="temp"
                             [loading]="temp"
                             [searchFn]="temp"
                             dropdownPosition="top"
                             placeholder="Select an instance"
                             [virtualScroll]="true"
                             formControlName="tempformname"
                            >
                    <ng-template ng-option-tmp let-item="item" >
                      <div>
                        <span popover="Lorem Ipsum text Lorem Ipsum text Lorem Ipsum text Lorem Ipsum text Lorem Ipsum text"
                              popoverPlacement="top"
                              [popoverOnHover]="true"
                              [popoverCloseOnClickOutside]="true"
                              [popoverCloseOnMouseOutside]="true"
                              [popoverAnimation]="true">
                          Lorem Ipsum text Lorem Ipsum text Lorem Ipsum text Lorem Ipsum text Lorem Ipsum text </span> |
                      </div>
                    </ng-template>