I am no seeing how TL makes any changes to the range of a jump drive based on the hull tonnage looking at the material in CT LBB 2 1977, 1981 or CT LBB 5 HG 2e 1980. The TL 14 J4 drive requires 6% of a hull's tonnage at TL 15 and the jump fuel requirement remains the same too.

A 300 ton hull + 100 tons of fuel in drop tanks equipped with a J4 drive requires 160 tons of fuel to make one 4 parsec jump. With the drop tanks carrying 100 tons of fuel in drop tanks that means the hull carries 60 tons of fuel internally. The fuel requirement for J1 = 40 tons, J2 = 80 tons, and J3 = 120 tons.

The 300 ton hull without the drop tanks using the J4 drive requires 120 tons of fuel to make one 4 parsec jump. The fuel requirement for J1 = 30 tons, J2 = 60 tons, J3 = 90 tons, and J4 = 120 tons. Using the fuel in the drop tanks and jettisoning them charges the drive to J3 and using 20 tons of fuel from the internal tankage charges the drive to J4 allowing one 4 parsec jump that lasts approximately 1 week. There is 40 tons of internal fuel that is enough to make a one parsec jump leaving 10 tons of fuel in the internal tankage and the trip takes another approximately week to cover five parsecs.

The 300 ton hull + 100 tons of fuel drop tanks with the J4 drive designed to move 400 tons 4 parsecs in one jump can move the 300 ton hull 5 five parsecs in two jumps.

Starting without the drop tanks the hull is 300 tons, keeping the 60 tons of internal fuel tankage, and J4 drive is upgraded to a J5 drive the fuel requirement is 150 tons to make one 5 parsec jump. The fuel requirement for J1 = 30 tons, J2 = 60 tons, J3 = 90 tons, and J4 = 120 tons.

Adding 100 tons of fuel in two 50 ton drop tanks increases the hull to 400 tons with 60 tons of internal fuel using the same J5 drive requires 200 tons of fuel to make one 5 parsec jump. The fuel requirement for J1 = 40 tons, J2 = 80 tons, J3 = 120 tons, and J4 = 160 tons. There is not enough fuel to make a J5 jump but there is enough fuel to make a J4 jump.

Sucking down the 100 tons of drop tank fuel first and jettisoning them when empty charges the drive to almost J4 and then sucking down 50 tons of fuel from the internal tanks is enough to make a one 5 parsec jump with 10 tons of fuel to spare.