On the RWS C225, because the rear adjustable sight is higher than the fixed version, the front has to be higher too. Though I don't know if it is the same sight for the Beretta, I would imagine the situation would be the same.
Frankly, though I did buy adjustable sights for the C225, in afterthought I think they were not worth the bother or the cost. At the time of purchase, I had not learned/found out that a pistol shooter uses an "area aim", rather than a precise "point aim" as with a rifle.
Save your money for some other goody and learn to use the fixed sights!
Walther CP-2 Match, FAS 604 & Tau 7 target pistols, Smith & Wesson 6" & 4" co2 pistol, Crosman 1377,
Baikal IZH 53 pistol, Gamo CFX Royal,177, Umarex SA-10 CO2 pistol.