TexasCHLforum.com

I'm uninformed about the 2017 rules draft, so don't trust me and wait for a real answer. But I feel pretty confident that the meaning is that each set of barrels is 3.5 feet from the center line of the course. The non-metric, conventional measurement is used above-the-line in the other measurements, and they do use either an apostrophe or "yd" to designate feet and yards respectively.

Seven feet doesn't seem like far to move, but it makes sense because the targets are still 15 yards away and are positioned roughly 20-feet edge-to-edge. They'd need to keep the angles fairly restricted for safety, and to keep the overall dimensions of the course reasonable for most clubs and ranges. If the barrels were 7 yards apart, that would put a pretty extreme angle on the outside target from each position.