So, having done around 350km since the fill up, I decided to take out the pump and see if I could get the piece out. After going through the getting the pump out joy, the fuel level was just below this piece.

I tried all I could without risking breaking something, it wouldn't come out. So I resorted to bending it in place, it is quite soft so after a few pressures on it, it seems to be in the right shape and angle (at least as good as I can get it while failing to get it out).



I also found the missing black tube, it was free in the tank, and the ending was just before the pump opening on the roof of the tank. I attached it back in place so it now is as it should. As it was, if it tried to transfer fuel, at least a part of it would not be transfered since it would fall on the flat top.

So now it looks close to as it should :



I should went and filled up as the tank dipped below a quarter this morning but its was pouring with rain with heavy winds so I gave up and decided I'd go another time

Before toying with the pump, Test number 6 read : (the car was not flat, angling to the driver's side)
18.0/ 0.7/ 18.8L
After :
18.3/ 1.1/ 19.4L

I'll go fill up tomorrow (if I get the chance) and see if it made any difference.