Tunemi, you just drew a line on the Earth and claimed that the observer could see the Moon behind the Earth's curvature over there. What is the difference between doing that and drawing a line over the North Pole and claiming that the observer can see the Moon on the opposite side of the Earth?
You need to figure out if the observer can actually see behind the Earth's curvature, not draw a line.
The argument you are putting fourth appears to be insufficient. We can also see that your observer's night horizon at Midnight is taking up more than a straight line 180 degree range from a top down view of that city, meaning that you are once again claiming that nights are longer after the March Equinox.
There is no curvature to be looked over.
The vertical and horizontal yellows indicate the centre point of the globe, and the position of the UK is to the left of the vertical. All the "curvature" will therefore be out of the way of a direct sightline. Simple geometry, Tom.
EDIT to include image
EDIT 2 for avoidance of doubt, the viewpoint here is looking at the night side of the Earth, along the Sun/Earth orbital plane, so the Sun would be directly behind the Earth illustrated here, along the centre of the horizontal and vertical yellow lines.
The grey dotted line showing the path of Blunham through the night is shorter than the blue one, which shows its progress through the day, so - shorter night, longer day. I have no idea how you are reaching your conclusion, perhaps you should rephrase this
"observer's night horizon at Midnight is taking up more than a straight line 180 degree range from a top down view of that city".
Clarify, please
Blunham's sunset before midnight was at 20.42, sunrise at 05.16 the following day. So at midnight, Blunham was closer to sunset than sunrise, so further to the left than the centre point indicated in yellow. Sunset was 3h20 short of midnight, with sunrise 5h16m after it. Midnight was not at the exact opposite of the sun