A process for modifying the melt index of a HDPE polymer in an olefin polymerization process, the process comprising: in a polymerization reactor, contacting (a) a polymerization catalyst, (b) ethylene, (c) an optional α-olefin comonomer, and (d) ( x + y) ppm by weight of an antistatic agent on an ethylene basis under selected polymerization conditions to produce a polyethylene having a target density ( d T) in the range from 0.940 to 0.960, and a target melt index MI t (g/10 min) in the range of 0.25 to 0.44 g/10 min; wherein x (ppm) and y (ppm) are greater than 0, and x is calculated according to the formula: MI t = MI c + ax; wherein MI c is a melt index (g/10 min) of a comparative polyethylene produced in the presence of y ppm antistatic agent under comparative polymerization conditions that are otherwise identical to the selected polymerization conditions, and wherein the coefficient a is selected from the following table according to the target melt index (MI t): Target Melt Index (MI t) a (For various target densities ( d T)) d T d T d T d T 0.940-0.946 0.947-0.951 0.952-0.955 0.956-0.960 0.25 ≤ MI t < 0.30 2.9 × 10 -3 3.4 × 10 -3 1.6 × 10 -3 4.6 × 10 -5 0.30 ≤ MI t ≤ 0.40 7.5 × 10 -4 2.6 × 10 -3 3.2 × 10 -4 2.2 × 10 -3 0.40 < MI t 0.44 N/A 1.7 × 10 -4 2.9 × 10 -3 1.9 × 10 -2 wherein the target melt index MI t is at least 20% greater than the melt index MI c of the comparative polyethylene, wherein the melt index is calculated according to ASTM D1238; wherein the polymerization catalyst is a chromium catalyst; and wherein the antistatic agent is an aryl sulfonic acid, a C8-C18 alkyl-substituted aryl sulfonic acid, a C10-C16 alkyl-substituted benzenesulfonic acid, a C10-C16 alkyl-substituted naphthalenesulfonic acid, salts thereof, or any combination thereof. in a polymerization reactor, contacting (a) a polymerization catalyst, (b) ethylene, (c) an optional α-olefin comonomer, and (d) ( x + y) ppm by weight of an antistatic agent on an ethylene basis under selected polymerization conditions to produce a polyethylene having a target density ( d T) in the range from 0.940 to 0.960, and a target melt index MI t (g/10 min) in the range of 0.25 to 0.44 g/10 min; wherein x (ppm) and y (ppm) are greater than 0, and x is calculated according to the formula: MI t = MI c + ax; wherein MI c is a melt index (g/10 min) of a comparative polyethylene produced in the presence of y ppm antistatic agent under comparative polymerization conditions that are otherwise identical to the selected polymerization conditions, and wherein the coefficient a is selected from the following table according to the target melt index (MI t): Target Melt Index (MI t) a (For various target densities ( d T)) d T d T d T d T 0.940-0.946 0.947-0.951 0.952-0.955 0.956-0.960 0.25 ≤ MI t < 0.30 2.9 × 10 -3 3.4 × 10 -3 1.6 × 10 -3 4.6 × 10 -5 0.30 ≤ MI t ≤ 0.40 7.5 × 10 -4 2.6 × 10 -3 3.2 × 10 -4 2.2 × 10 -3 0.40 < MI t 0.44 N/A 1.7 × 10 -4 2.9 × 10 -3 1.9 × 10 -2 wherein the target melt index MI t is at least 20% greater than the melt index MI c of the comparative polyethylene, wherein the melt index is calculated according to ASTM D1238; wherein the polymerization catalyst is a chromium catalyst; and wherein the antistatic agent is an aryl sulfonic acid, a C8-C18 alkyl-substituted aryl sulfonic acid, a C10-C16 alkyl-substituted benzenesulfonic acid, a C10-C16 alkyl-substituted naphthalenesulfonic acid, salts thereof, or any combination thereof.