I have flop tubes in both tanks and mounted the senders in the rear tank baffle in one of the outboard bays. You will need to pull the tank no matter what you do, so where you put the sender will not be much of an impact. As I recall, the -4 plans show the recommended sender installation location for a tank with a flop tube.
Unless you are planning to do negative G aerobatics, flop tube(s) may not be necessary. Do you have an inverted oil system?
Good luck,
Dean