  The amplitude for the forward electroproduction of two light vector mesons
can be written completely within perturbative QCD in the Regge limit with
next-to-leading accuracy, thus providing the first example of a physical
application of the BFKL approach at the next-to-leading order. Recently, a
numerical determination of the amplitude has been obtained in the case of equal
photon virtualities, by using a definite representation for the amplitude and a
definite optimization method for the perturbative series. Here, we study the
main systematic effects in the previous determination, by considering a
different representation of the amplitude and different optimization methods of
the perturbative series. Moreover, we compare our result for the differential
cross section at the minimum $|t|$ with a different approach, based on
collinear kernel improvement.
