Can't answer the question posed but in terms of seeing things at a distance...
While sitting high up on my local common in south London on clear winter days after sunset, I can see sun lit vapour trails right down on the western horizon. With the aid of ADSB I have often been able to work out which aircraft they are and the furthest I can see them is about halfway across the Irish Sea and down beyond Truro. This last observation was confirmed by a Martinair 747 which passed over me and its trail was still visible as it passed abeam Truro which is about 230 miles. Another good one was a Ryanair 737 out of Cork to Gatwick; spotted the trail abeam Milford Haven and watched till around Dorset when it disappeared as it began to descend. I probably could have seen the lights as it flew the approach onto 26 at Gatwick, but 30 mins or so after sunset it's beginning to getting a bit dark and I have mile of common to cross with attendant tree roots, cow pats and other unpleasant hazards in the grass!
During Lockdown with fewer aircraft about, one lengthy trail stood out in the early evening NW sky with a couple of turns in the trail, I spotted it abeam Chester and followed it down past Brum to London where it turned east heading towards Europe. A FedEx aircraft out of Dublin.