The space-charge-field amplitude inside photorefractive crystals was evaluated using three different experimental techniques: (i) two-wave mixing gain measurements, (ii) direct phase demodulation under external dc-electric field, and (iii) phase demodulation under ac-field with proper polarization filtering. The experimental data could be simultaneously fitted with the theory in the frame of the traditional one-level photorefractive model only if an additional reduction of the space-charge field is assumed. The traditional model fails to explain appearance of this reduction factor. Measurements were carried out with Bi12TiO20 and GaP photorefractive crystals