I figured it out! I have successfully done this repeatedly and failed when deviating. Note that number of battle below is 1 less than win count on screen.
3v3 1-3 stars:
9... 3 star max or 3.5k total PI
3v3 3-4 stars:
1-13 whatever. sand bag if you must (10-12).
14-15 4 star rank 3 or higher.
16... 3 stars max or higher no less than 5k total PI
3v3 1-5 stars:
1-15 whatever. sand bag if you must (10-16).
16-18 4 stars rank 4 or higher
18... 4 stars rank 3 or higher (mix 2x4 stars rank 1x2)
3v3 4-5 stars:
Sorry I only have 4 star rank 4 and lower. The requirements are too high for me.
(observation) It seems to me, when the easiest option is double your total PI is when the infinite starts, but it wont kick in unless you have high enough PI.