I was doing some testing on some scenery tiles I had created and wanted to get my head around how the tiles work together. So I decided to find out the distance you are when a tile appears for a particular GeoConvert level.
Listed below are the approximate distances a tile will appear at:-
. A level 11 - 40nm
. A level 12 - 20nm
. A level 13 - 8nm
. A level 14 - 6nm
. A level 15 - 1nm
So a level 11 tiles becomes visible at 40nm away as you fly towards it, and it disappears as you move more than 40nm away. This draw distance does not appear to be affected by altitude or speed.
Now the bug. If you load your aircraft say 50nm away from your level 11 tile, it comes into sight at 40nm. However if you load your aircraft at 90nm away from the tile, the tile will only appear at about 10nm. instead of it usual 40nm. This test was done in the F15 at about 30,000ft and max thrust, but I did a few tests at 300 and 800 knots and found speed wasn't issue.
I also tried it with a level 13 tile which normally appears at 10nm. Starting at 40 nm away the tile appeared normally at 10nm. I then tried 50nm and the tile also appeared normally. However when I exited FS2 and went back in, the tile appeared at only 4nm when starting from about 50nm.
So it seems to be a combination of distance from the tile, the draw distance of the tile in question, and whether you have used the scenery in the current session.
I did read in another thread (which I can't find now) that users were reporting that the latest update had introduced a bug that was causing tiles to pop in later than they had in the past. Not sure if this is new or has been around for a while, but my findings might indicate the scenario that is causing this issue for some users.
Note: these test were done on a single tile of level 11or 13 tile I had created using the wiki scenery process, and loaded in an area with no default imaging other than fuzzy global.