Comment on “The new FL measurement from HERA and the dipole model”

The upper bound on the ratio of the proton structure functions FL/F2 tested in the recent paper “The new FL measurement from HERA and the dipole model”, contrary to what is said therein, does not provide a model-independent “rigorous” experimental test of the color-dipole picture. The validity of the theoretical upper bound depends on an ad hoc assumption on the dipole cross section. The analysis of the experimental data in the paper “The new FL measurement from HERA and the dipole model” can be reinterpreted as an additional confirmation of the absolute model-independent prediction from the color-dipole picture of FL=0.27F2 at large Q2.