get _overflowButtonEffectiveWidth() {
      const button = this._customOverflowButton ? this._customOverflowButton : this._overflowButton;
      // if in "Group" mode overflow button size is equal to the offset from second item
      if (!button) {
        return 0;
      }
      if (this._isGroup) {
        let item = this.items[1];
        const ltrEffectiveWidth = item.offsetLeft - this.offsetLeft;
        // in some cases when second avatar is overflowed the offset of the button is the right one
        if (!item || item.hidden) {
          item = button;
        }
        return this.effectiveDir === "rtl" ? this._getWidthToItem(item) : ltrEffectiveWidth;
      }
      return button.offsetWidth;
    }
Return the effective overflow button width
Differences are that when in "Group" type the button is offset and overlaps the avatars

1) In case of "Group", (LTR/RTL aware) button width is qual to second item offset left/right
2) In case of "Individual" group type width is directly taken from button element
@private