To treat the TK# has halved would treat the FT as firing at long range, which this unit does not have. Since the rule does not give long range capacity to this FT, you should not treat it as long range for any purpose.
Recognizing that reality plays no or very little role in rules interpretation, halving the TK# for this FT would treat the ability of this unit to kill a tank worse than a MOL. The TK ability of this FT (as well as the FP) is dependent on the ability to push flammable fluid. Velocity and arc determine distance. A homemade FT is certainly more lethal than a MOL to a tank.
Neither the rules as written nor logic support the halving of the TK# in this instance.