Mean excess return v/s three factor model predictions. Based on the following figure, explain if the model works well in predicting the returns of the underlying portfolis

FIGURE 5 Mean excess return vs, three-factor model predictions A. Changing size within book/market category Notes: Average returns versus market beta for 25 stock portfolios sorted on the bass of size and book/market rato versus predictions of Fama-French three-factor model. The predictions are derived by regressing each of the 25 portfolio returns, Rp, on the market portfolio, Rtm, and the two Fama-French factor portfolios, SMB,(small minus big) and HML, (high minus low book/market). (See equation 4 in box 1 .)