I've copied and slightly edited that post to here for ease of reading and in the hope of generating discussion whilst avoiding any hijack of Marks excellent Roach Reflections video thread. I hope that's OK with all. If not just PM me and I'll remove it
I'm always thinking about how the hook and last few of inches of any tackle are positioned and perceived by our targets. This has perhaps been bolstered by my long time fascination with fishing the fly for fish of all species. Swinging a fly downstream for salmon in England these days certainly gives a man plenty of time for thinking
but ours is the contemplative sport after all
So here's a few of my thoughts and observations....
The flow of water can be very laminar, vary greatly within the water column and is subjected to great variation in its path downstream. Our perception of currents from looking down from above the surface and the effects on tackle and particularly the hook are not always borne out when observed by snorkeling and following a cast or trot along its length. A colleague and I experimented with fly, nymph, spinner, plug, rolling lead, feeder and various float tackles in high summer over a period of setled low flows and clear water. We learned a great deal and were quite surprised at how our perceptions as life long anglers were in some cases quite wrong! I got serious sunburn on my bald spot and on the areas where the wetsuit met exposed skin but that's another story....
We used stick floats shotted shirt button style, a range of avon and bolognese floats to 6g, a range of Topper Haskin crow quil avon and giant wire stemmed floats to 30g and pike/sea floats carrying up to 90g of lead. Tethering a bait to hook and tackle or a fly to line and leader changes the reality of how it travels tremendously. Experiment showed that only if holding a float completely at a stop with surprisingly heavy shotting, and then allowing the float to travel very slowly by holding back hard, can even an unbaited hook be expected to travel downstream in front of the tackle on the expected line and depth in anything remotely like the J shaped curve of those many diagrams. More often it's skewed off to one side and/or the bulk and tell tale shot is ahead of the float but the hook is not where expected! If there's much line between the bulk to the tell tale and on then to the hook, or those shot are not heavy enough, then our hook can be wandering well above the expected depth and/or way off to one side. Allow the same set up to run through at the rivers pace and the hook behaves very differently again as it and the rest of the tackle are variously pushed pulled/dragged down river. Add a bait and that changes everything - travel and movement, reaction to the micro currents and vortices etc created by river bed topography, etc. This altered depending on bait hydrodynamics in the form of size, shape, density/buoyancy etc as well as movement eg lively lob worms could add a mad dance under their own propulsion.
There can be a surprising amount of windmilling, spinning and swirling of lighter baits like corn, caster, maggot and bread and there's plenty of stop/ start stuttering on top of that - all whilst the float moves steadily downstream as observed by the angler.
Is this why we find certain 'hotpot' areas in swims - as much because right there and for that length our presentation becomes acceptable or more in line with the flow of loose feed as much as any other factor?
There's another chapter to all of this and that's the behaviour of the fish in the way of resting, feeding, shoaling, competitive vs defensive etc ...maybe later on that as I've developed square eyes!