Just my personal experience Rich but which has brought me some good fish...Question.
Steve others. You mentioned bait placement. I cannot remember taking a Barbel quickly when fishing for them, have you? It makes me think about lots of things, are the Barbel not in that swim, and I've baited them into it over time? Are they in situ but I scare them with tickled bait, or they take time to get confident eating it.
Spooked Barbel will not gradually be enticed to feed because they've gone, spooked, aren't there anymore hence my comment...
Bear in mind that I apply this to low water conditions and situations where the fish are generally more wary, such as more pressured stretches of river and aside from this I fully subscribe to the theory of the feeding before fishing concept in order to build up their confidence... I reckon it was Steph Horak who was an advocate of this as far back as the 80's although I'm sure it went on long before that.Naturally, during daylight at least, the fish are even more cautious than usual and to the extent that loose feeding (or introducing feed via any other method) could well result in spooking them.
I say subscribe to the theory as I rarely ever do it if I'm honest.
Bait placement is another thing altogether and as I mentioned I would struggle to describe it but Graham will know what I mean from a certain swim we've shared in the past, the underwater current goes in the opposite direction to that on the surface and only by freelining a bait will you ever know as a lead will obviously tether a bait regardless.
Watching your line, where it enters the river, moving in the opposite direction to the surface flow is a bit weird but...
There are two positives from this, firstly by freelining there is no lead or feeder to snag up and in the swim in question it allows me to fish in areas where most people flinging a lead or a feeder would give up after several re-rigs due to snagged gear.
The second is that the bait comes to rest in natural collecting areas for food and areas which aren't that obvious going by the surface flow.
On the subject of quick bites I've had one or two where the bait has literally just hit bottom but I put this down to luck and landing it on a fish's nose on one of those days when they're just having it, it's rare (for me anyway) in general although I've had many within five to ten minutes of the bait resting up and that's without feeding and applying the theory that I've described.
I honestly think it sorts the bigger fish out too, if you think about it the bigger the fish the more they have to consume and by the time they reach a certain size they must have seen it all so doing something a little different could just tip the balance in your favour.
As for crust being some sort of wonder bait...
In those circumstances I would say a very definite YES!