I currently set up courses that are in the 26-30 TDF range. And I've begun to do so with with no targets having Kill Zones smaller than 3/4".
We're currently seeing two classes becoming predominate, Hunter and WFTF. There are some open class shooters that shoot with us too but right now, these two make up the bulk of monthly matches.
Rarely do I hear any KZ size complaints. Most of the difficulty in my courses is made up in distance. IIRC there were two targets that were what I would consider challenging from a KZ perspective. One was a 3/4" at close to 30 yards another was 1" at 40 or so. I can't remember the distances exactly. We only have 5 sizes of KZ 3/8", 1/2" (both via reducers), 3/4", 1" and 1.5", and most of the time I only use the three larger. But to my knowledge, no one has cleared any of these during an actual match.
I'm fortunate in that I have a lot of varied terrain features to use. Slopes, trees, hills, etc., make up a lot of what I build into course difficulty. You can't really put it into a form or spreadsheet. For example:
I'll set two targets such that the KZ's are visible but not the entire target from one specific spot in the shooter's position, using tree trunks to block one of the targets if that one lateral position is not realized. But I'll open up the width of the lane to encourage that person to make a seating change. Usually, that break in position will equal a break in concentration, even if timers are not involved.
If they are wanting to be better marksmen, then lessons will be learned. And if they don't, then it doesn't matter anyway but it still makes for a fun match because there's not a target out there that doesn't feel doable by most.
But I love setting up courses. I think I like it better than shooting the course.
Anyway, good post subject. A course doesn't have to feel impossible to be challenging.
Map to the FT Park> http://maps.google.com/maps?hl=en&q=1150%20Evans%20Bridge%20Road%2C%20Heflin%2C%20AL%2036264