Apologies for the digression from the hooks thread, though hook choice has to made in context to the material & means that it's connected to the mainline to get the most from it..!
Rigs, it's a confidence thing. There is no need to change them unless one believes there are issues, other than watercraft, that is resulting in hook bait pick ups not being converted into takes/runs.
I have been fishing for over 30 years, carp fishing for 20 of those years & only 7 years for barbel on bigger rivers. I am a firm believer in what Adrian advocates and that is to keep things as simple as possible. To some, what I have written is probably a bit removed from simple, but to tie that rig is simple & can be accomplished in less than 5 minutes. The combi rig is simple, the mechanics of it are common & fundamental to many modern anti eject rigs.
From my point of view, a bait that has been picked up by a fish should result in a run. In reality this is not always the case. To prevent this we try to ensure the bait is first taken into the mouth and to maximise this opportunity by converting this into a hook up.
Regarding the combi and the length of braid tail we use. Firstly, like most stiff natured rigs, good presentation relies on that it is used on a relatively firm, flat bottom clear of debris. If this is not the case then this rig will not lie so flat and will have the tendency, at least in part, protrude from the bed. For me, possibly the only advantage of having an extended braid tail would be to slightly negate the potential for this protrusion.
Regarding the use of braid to confer a softness that a fish cannot feel when the hook bait is taken. This was in part the original school of thought in the 1980s for the use of dacron. For me though, for a fish to have ('not') felt this softness, the fish has had to have come into contact with the braid - has it bumped into a part of it or has the fish actually taken the bait? Given the latter (and that the rig is mostly flush with the bottom) the bait is in the mouth then its a matter of turning that hook before the fish has the time to completely eject the rig.
By lengthening the braid this, for me, makes it easier to eject the hook bait. There is greater clearance between the hook and the monofilament. Whereas with a length of an inch there is enough movement for the free passage into the mouth yet on ejection of the bait the stiffness of the monofilament keeps the tail end more within the mouth for slightly longer so allowing the differing stiffness's of materials used to help the bait topple/tumble within so increasing the chance for both the hook to turn and so giving better hooking potential.
When fishing over a bed of particles I feel that fish have their heads pinned down closer to the bed not having to move as far for the next bait and again this shorter length helps turn the hook quicker in these instances.
I completely agree on keeping things as simple as possible. Whilst reading books from more accomplished anglers than many of us, there is comparatively little emphasis on rigs compared to the rest of what they are trying to portray.
For my barbelling, I have 4 standard rigs with some slight variation dependent as to what baits I want to use. One of my most successful rigs I have ever used is just a size 6 super specialist attached to an eight inch 8-12lb monofilament, the hook being wrapped in a very soft water based fish meal paste.
As for changing ones presentation, the ability to see the fish react with our hookbaits baits is the best privilege we be afforded. For me that is not the case. If I knew there were feeding fish in my swim yet I was not getting the amount of takes that I would expect, negating all other considerations, I might tweak a rig. Normally I'd change either the size/type of bait (with this sometimes change to a suited rig) and/or length of rig. If this carried on being the case then deep surgery with a bit of experimentation might ensue, which even if this does not result in more fish makes sure that I am optimising most aspects and trying to think a little more out of my normal box which can only be a good thing.
Its the obvious proviso, get the location & approach mostly right then hooking the fish is the simplest part of the whole.
Cheers, Jon