My personal thoughts are that they are a valid target. It fools the shooter into thinking they have a easy target, especially when a reducer (25mm ), and it does sometimes cause that person to 'switch off' a little bit and then you get the dink of a miss.
Weather conditions do play a part as well. I can remember settign a course up in the early 1990s (94 I think) for our 1st ever WL shoot for the CSFTA and finding that the weather conditions were going to be windy (put a very in front of it) brought a few targets in closer. This was in the days of 30 shot courses. A shooter said that the targets were to close and needed to be moved out, the captains decision was it was to stay as it was.
This shooter, apologised after the shoot as he had never shot a course so difficult due to the wind. He said that when he missed an 8yd full size kill on the first lane he was glad they were closer. The top score for the day was 13 and after that we got a reputation of difficult courses due to wind.