What is the test for establishing probable cause in a sealed affidavit?

In People v. Seibel, supra, 219 Cal.App.3d 1279, 269 Cal.Rptr. 313, the court was presented with an affidavit that had been sealed to protect the identity of a confidential informant. Defendant was denied access to the material facts the prosecution was relying on to establish probable cause. The court recognized that the defendant could not reasonably be expected to make the preliminary showing required by Luttenberger. It then held that once the court determines the affidavit is properly sealed, it "must then treat the matter as if defendant has made the preliminary showing and must hold an in camera examination as required by Luttenberger. Because in sealed affidavit cases such as the one before us the defendant may be completely ignorant of all critical portions of the affidavit, the defense will be unable to specify what materials the court should review in camera. The court, therefore, must take it upon itself both to examine the affidavit for possible inconsistencies and to inform the prosecution what materials or witnesses it requires.... [p] Because the defendant's access to the essence of the affidavit is curtailed or eliminated, . the lower court may, in its discretion, find it necessary and appropriate to call and question the affiant and/or the informant, ..." (Id. at pp. 1297-1298, 269 Cal.Rptr. 313.)