...
2. At the time of writing his investment would represent
a share of ~15 % of the total bankroll (1000 BTC / 5539 BTC (currently invested) + 1000 BTC (his investment)).
...
Actually these numbers would be slightly worse, because the 20 BTC dilution fee
would be part of the total bankroll as well.
I should have used the following calculation:
980 / 5539 + 20 + 980 = ~0.148 %
It's my understanding that the dilution fee is applied right after NOT right before the investment, therefore a new investor will get part of his own dilution fee back, which is important for a large investor.
Example: whole site bankroll is 1 btc, and you invest 100 btc, you will get around 1.99 of the 2btc dilution fee back right away.
Good luck with the girl.