I have small bags I use on my personal 19fter. The front I tie off a cleat just in front of the wind screen, bags sit just behind the back to back seats, basically where the boat is a full beam. I use them even in summer at speeds where the kicker would run by itself. I have more control with the rpms up and more thrust. I do tie the rear as well so the cant get too far off to the or under the boat in turns.

In some wind and wave condition I will pull 1 bag to counter act the effects of the push.

I also like how it helps pins the bow down in rougher waves.

I find I use them more for boat control than speed controll

Placement along the side could very dramatically effect how the bags pull. What size bags do you have, with a smaller boat several size bags might be needed depending in speed, current, conditions.

Not sure why your fish would be getting under your bags when coming in, but a simple turn when the fish is 20 ft or so away corrects that