It is worthwhile remembering that prosecution during the international phase of a PCT application is effectively national prosecution of the application in countries designated by the PCT application.
This means that amendments made in an attempt to achieve a "clear" written opinion can subsequently be rejected during national phase in countries such as China and in Europe. Those jurisdictions have strict prohibitions on the introduction of new material by amendment.
For example, the PCT application may have a broad generic description of an aspect of an invention while the description of the preferred embodiments may have a specific description of an embodiment of that aspect. In such a case, an amendment introducing an aspect that is broader than the embodiment but narrower than the broad description may lead to a clear report here, but may very well be rejected when the application is examined by the Chinese and European authorities.
Thus, the specification filed with the PCT application should include as much description of alternatives as possible. Use of generic language of varying scope is important. The attitude of your patent attorney should be one of anticipating and expecting the need for amendments two to four years after the PCT application is filed.