Hey One Dog.
You're fine with that.
I fish 6 rods with flashers sometimes spaced as close as 10 feet between stacked lines, with 3 per side of an 18.5 footer. The trick is to make sure that you are going a good speed when letting your rigger down, and having a long enough lead off the clip so that they don't tangle.
When fishing without flashers, I have run them as close as 6 feet when fishing a narrow depth. I remember one day fishing Cowan's Pt. several years ago on a charter boat when we had six rods available, and I had 3 per side, 10 feet separation, and leads of 12 to 25 feet of the clip. I had one rigger at 120 and the other rigger at 145. In the span of 2 hours we had 5 fish between 7 and 14 lbs. That was a memorable day.
On the other case , when seeking out where the fish are, a 20 foot separation is more than sufficient.
I know a guy that fishes 3 rods off his boat which is a 16 foot Double Eagle, and all 3 are on the same rigger. He usually fishes alone. He uses a 15 lb ball, runs the first line with about a 15 to 20 foot lead, drops it down 25 feet, clips the second rod on, same lead off the rigger, lets it down 25 feet. then walks the rod over to the other side of the boat (behind the boat of course, clearing his outboard) puts it in the rod holder. Then he readies his third rod, and clips it on runs it back 20 feet, and then lowers it to the deepest depth he wants to fish.
Thus, the effect is that he fishes a 75 foot spread.
Thus if he is fishing 130 feet down, he has another line at 105. and 80 feet.
As you can imagine...it's not all that bad, especially if you are fishing for feeder springs off Cowan's Pt, if you get one fish on, you stil have 2 more lines fishing, and you can keep right on troling and potentially hook and land a second nice fish, and then pack it in for the day!