One thing you have to remember is that you are not starting the banking from scratch, you have done prize missions in the past and have received rewards from them. So when you do start backing you may already be in the positive or could need to pay back a lot. To add further complication of the process, plarium introduced random variables into the algorithm that determines your reward, or whether you are or not. Even if you have banked millions, there is still a chance that this algorithm could determine that you will not be paid this time, you bank balance is still there, its just they are refusing to pay this time.
This is what they posted on the Total Domination forum back in early July of 2014 regarding the algorithm, I consider it to apply to Pirates as to my knowledge and from experience, the payout algorithm is virtually the same for each game.
We don’t share the exact algorithm for the feature, but here’s the basic outline: every time you attack or defend a [prize], your unit losses are totalled up according to each unit’s price in [Rum, Gold, Lumber]. This running total is your Payout Number. When you get payout from a [Prize], the spread, number, and type of Units or Resources you receive are randomly allocated as measured in resources based on that total.
The longer you go without receiving a payout, the higher your Payout Number total is becoming and the bigger your eventual reward will be (that's if you continue to bank). Now, there are also some randomized triggers when running this calculation – first, it does a “spin” to see if this infestation will pay out this time, or just keep adding to your Payout Number. Depending on how this spin goes, it’s possible to go extremely long periods without getting a payout (even though your Payout Number is still growing over time). This is especially true if you've received big payouts on higher-level [Prizes] and then go back to hitting low-level ones.
The payout frequency is a little higher for the [prize] that pop up directly on the left side of your screen, but those require hitting consecutively higher [prizes] each time. Sometimes you can also “spin” and hit a superbonus, which will trigger a payout worth more than your total investment, but those don’t pop up much.
The biggest misconception is that regular [prizes] each have their own discrete payout amount. I know it often seems like we’re laughing maniacally to ourselves as we change each [Prize] Level’s payouts every week to confound everyone – this isn't true. It doesn't work that way.
The payouts are based on your collective Payout Number; the last time you triggered a payout, and how many Unit losses you've suffered in the meantime. Treat it like Black Jack; play with a long view, don’t bet everything you have, and quit when you’re ahead. It can be frustrating, but senior players have experimented with different strategies and gotten pretty good results. Ask around, but be prepared to lose a lot of troops to get there – don’t commit anything you’re not ready or able to lose without being hamstrung.
Some advice: take advantage of Global Mission events to “double dip” on your investment. Also don’t forget to include the XP, and Ranking Points, ranking awards, Achievement Bonuses, and other freebies you’re getting from taking on the Infestations.
Also, if you want a sure bet, don’t forget about the Campaign [Prizes]. Each one of these has a fixed payout in [Brethren] units that you can view before deciding whether or not to run the mission – plus they all have a pretty cool storyline and audio content, but the higher ones get really, really tough.
In the coming months we’re planning to experiment with the payout frequency algorithm to make it a little less discouraging from the player end, so standby for future announcements.