Recently, methods have been developed to characterise the relative amounts of crazing and non-crazing processes which occur in rubber toughened glassy polymers, using the invariant obtained from small angle X-ray scattering (SAXS) analysis. In this approach, however, the influence of the deformation of the rubber particles has previously been ignored. In this paper we explore how deformation of a three layer core-shell rubber particle affects such analysis. It is shown that, for a submicron rubber particle system, the form factor makes a significant contribution to the SAXS pattern, and the intensity of this scattering increases as the concentration of rubber particles increases. The details of such form factor scattering are frequently inaccessible, as the scattering occurs at very low angles. However, various extrapolated forms for this low q scattering have previously been assumed in order to calculate the amount of crazing by suitable subtraction of it from the experimental data to yield the appropriate invariant. Since the form factor may change during deformation, as the particles change shape and internal debonding or cavitation may occur, subtracting the scattering from the undeformed form factor may or may not be an adequate approximation. This paper tests the validity oi the approximation. It is shown that, for our particular system, the length scale of the internal morphology of the rubber particles is comparatively large compared with the size of the crazes, and the effect of the particle deformation is indeed fairly minor. However, it is clear that with other systems, a changing form factor may overlap significantly with the peak due to crazing. This effect will then become significant and must be taken into account.