Offshore Planer Boards - Can’t always detect bites

I spent the entire season trolling on my home lake with a lot of success. I was always pulling size 5-9 flicker minnows and flicker shads using the 50+2 method. I often catch fish and get no detection (flag down, board falls back), I even watch the rod tips and note that they’re vibrating. At the end of my run, I’ll pull in the lines and often pick up a walleye.

Most walleye in my lake are between 12 and 20 inches. Most times when this happens it’s on the lower end of the scale but I have dragged 18” walleyes for a while without knowing it.

I increased the sensitivity of the flags and it hasn’t helped much. What else can I do to get better feedback on hooking fish with planer boards?