Don't really see where you are going with this. Everyone's performance here has changed by the same amount, so nothing to do with the install.
Overall signal is now down by 1dB SNR on all transponders compared 4 months ago. If it drops much more everyone in Torrevieja with a 1.4m offset dish is going to lose BBC/ITV.
The install is not the problem, and Joddle if the two satellites where right next to each other (so you could reach out and touch each other) then they would preform the same way, but they don't, there are 7 satellites (active) at the 28.2 degree orbital location an they have a maximum/minimum separation distance of 250 to several thousand miles, they may look to be at the same co-ordinates but they are not.
This maybe one reason you would/could see a difference in performance between the 2E and 2F satellites. (
but my bet is on a ground or ocean bounce off a temperature inversion layer, if the elevation of the dish is just right you pick this up and it causes a drop in signal)
These satellites are 22,500 miles out traveling at 17,500 miles per hour, this puts them in a fixed location over one spot of the Earth, and due to the receive beamwidth or your satellite dish you can pick them all up at once when pointing to the 22.2 degree orbital location.
And they do not play around with the transponders power level, nor can they adjust the spotbeams, these are fixed shotgun antennas on the satellite pointing at a fixed location, they do not move, adjusting one would affect all.
Most of the satellites up there do wobble a bit, and this could be the problem, this wobble is due to solar wind and other things affecting the Earths magnetic field and gravitational field, this can cause a wobble in the satellite, then the satellites gyro stabilizers have to correct it, in extreme cases they may have to use the satellites stabilizing jets, but they do not want to do this as it uses fuel, and they only have so much fuel on board.
And one other thing that could affect them is the Moon, if it can cause the lunar tides, it can affect the geosynchronous satellites, and this effect can be at a certain time of day, month or year.
So there are lots of forces out there affecting these satellites.
All these effects can be compensated for by going to a larger dish, we in the broadcast industry know about all these effects and use very large dishes to compensate for them, for "C" band we use 6 to 10 meter dishes (this depends on the satellite and location) for "kU" band (if needed) we use 3 to 6 meter dishes, (again depending on the location and satellite)