We have passed this matter to the Devs and on initial review they have confirmed this is not how the system works and the theories above are not correct.
We hope to have a detailed explanation in the near future. The Devs are currently very busy with the next major update. But the points above are not reflective of the current system.
Some more detailed explanations from our development team
Thesis: The caveat to this is: if you get your useful action at 10 minutes into the 15 minute timer... From 10 minutes onwards will be counted as participating in your useful action.
This means, from 0 minutes to 9 minutes you did not make any SL.
Developer Сomment: Absolutely not. The calculation takes place once after 15 minutes or less, if the player has lost a vehicle or the mission has ended. All actions within the interval are equivalent and are considered in aggregate, regardless of the time when they were performed.
Thesis: So for instance, if you have a plane that makes 1000sl every minute, and you get a kill 10 minutes into the timer. You made 5k sl for that 15 minutes.
Developer Сomment: If you have an aircraft that makes 1000 SL per minute and you made one kill, which brought you 450 score points (with zero BR difference), this means 79% activity in a 15-minute interval. And your reward will be 1000 * 15 * 0.79 = 11850 SL. From which 20% is deducted as part of the landing reward that you receive upon a successful landing. So, you will receive 9480 SL immediately, and 2370 SL will be assigned to you until a successful landing.
Thesis: If at the end of the game, you have a 75% participation, it will take that 5k SL from your Useful Actions and multiply it by .75 This means you really made. 3,750SL.
Developer Сomment: The reward for each interval is calculated immediately after its end and does not wait until the mission ends. The final activity in the mission does not in any way affect SL earnings in any of the game modes, except for PvE.
Thesis: Getting a useful action after the first minute only decreases your reward.
Developer Сomment: Of course not, any action can only increase your reward. Or leave it unchanged if you have earned enough score points to achieve maximum activity in the current interval.
Thesis: Posting evidence with explanation below: in the spoiler.
Developer Сomment: Your 153199 SL are made up of 3 intervals of 15 minutes:
1. 2207 score points and 42106 SL,
2. 1010 score points and 41612 SL,
3. 1694 score points points and 42099 SL,
and one 641 second interval at which the mission ended:
4. 800 points and 27382 SL.
Total reward for useful actions is: 42106 + 41612 + 42099 + 27382 = 153199.
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