Why not do the following instead which would be equivalent and simpler.
The output will be automatically set from the value of your :file header
argument.
#+begin_src gnuplot :file fig/transInc.eps
reset
set encoding utf8
.....
#+end_src
That kinda works, but I think you still need to set the terminal type within the source block. Using the above the command "set terminal eps" gets sent to gnuplot, but you actually need "set terminal postscript eps".