DGrant eyes are good, if you look at ground level you can see many things at that distance eg when you are driving past a known flying field I can easly see the aircraft in the sky they might only several hundred feet in the sky but you are still I km from the field once your eyes are in focus at that distance . Of intrest I often look for Planets in the day light ,they are not easy to find but I have achieved this several times. the method I use is to look at the night sky and watch the moon when the planet is close then in the night sky find the moon and look to where the planet should be.Its not easy but can be achieved . and also pick the brightest planet
As to the gear I use hitec aurora 9 with the tele the reason I have the tele is I lost one butterfly for 3 weeks with a band new OS 20 FS that was something that was not going to happen again. I even had a mate fly over the area looking for it with no luck.
As to my eyes I have just started to use glasses to read the news paper,they are a better set than the usual for a 68 year old.
When I went to that height it was straight up and then straight down and the transmitter was set to above take off point not sea level
as to range never had a range problem even when it was lost it still showed the receiver voltage on the transmitter . Jets to fast and expensive and I'm not that good a flyer yours Paul T