Backleads affect sensitivity and bite indication and I avoid them unless absolutely necessary. As soon as the lead is on the deck you have a hinge point, and that means a decrease in indication. Slack lines are much better for indication at shorter ranges (up to 30 yards) but at longer ranges they, too, are not that great.
For almost all of my fishing I go semi-tight. As long as you use heavy lines or even drop a bit of putty on the last 12ft or so, they should sink well enough to fish effectively but not too slack.
Have a think about why you need a backlead at all. In the edge slack is better, at medium range fish semi-slack with putty, and at longer range you don’t really need them as the line is near the deck anyway.
Putty isn’t just useful for hooklinks, blob some above the lead too
If it’s purely to avoid boats, get your backlead as far out as you safely can, fish a tight line between the leads, use a heavy old bolt rig and hit any single bleeps you get.
Backleads are a must to avoid boats but use a heavy bolt rig and hit any indications!