Actually, I thought about it too because the ratio of 1/2 I noticed was too strange to be random, and that because I already completed the outbound segment (basically half of the trip), the SAF offered to me was only for the remaining half of the trip.

But I read (forgot where) that the Environment (AF)/CO2ZERO (KL) option with SAF was purchasable at any point in time during the trip (as long as it was not already completed), and the various gradual options offered were always based on the offset for the total trip.

This is why it doesn't really matter whether you click on the Environment/CO2ZERO option for the outbound flight or the return flight, you were redirected to the same Options selection screen (Seat Selection, Baggage, Environment) where the SAF is calculated on the total trip with the various offset selection (10%, 20%, 100%).

To be honest, I am quite happy because I thought the pricing that AF gave me initially ($700) was a bit steep, and the options offered were only 3: $30, $70 and $700 with nothing in-between. Maybe AF/KLM should offer more in-between options with a sliding bar where you can move the cursor anywhere between 0% and 100%.

On a different topic, anyone knows if everyone in the same booking can purchase the SAF Option or is it only possible for one person? I am asking because on the KLM app, like the AF app, the view of the various options changes depending on the passenger in the reservation (seat number, meal selection etc...).

When I click on my name, the CO2ZERO option button shows "Contributed. Thank you!", but when I click on my children name or my husband, it sats "Contribute" but when clicking on it, only the Seat Selection and Bagage options show up, not the CO2ZERO/SAF option. Is it a bug?