There are other factors *, but this was the basic calculation.
*) May I point you to the thread of this post?
IMHO, if you want to cut your average, it's better to play 9 hole rounds.
1) You get two scores instead of one,
2) As you recognised, chances are that one half is substantially better than the other. You'd take much more profit from the (doubled) better half alone than from the merger of both.
3) You are more flexible in playing different courses. IIRC, you play a lot on STA - go and learn and enjoy the others, too!
Furthermore and in general, it's good to play 9 hole tournaments to receive more XPs. Not for you because L93 is quite elevated for a Master.
Anyway, take your time and have fun!