I tend to use liquidised bread when fishing swims with not too much flow and supplement it with pinches of bread flake of the same size I'm using on the hook. That way you're giving the fish a real sample of your hookbait and not just a taste so that they can latch on to exactly what to look for to get the best feed, ie, make them hunt around for the hookbait amongst the crumbs.
You have to make sure you pinch all the air out of the flake or it won't stay put for too long.
Using a percentage of mash in the liquidised is a good idea but I prefer to just dampen the liquidised a little with a spray of flavoured water to make it stodgier, how much according to the swim I'm fishing, but more stodgy for faster and deeper water.
Also control the feed by swapping from a cage feeder (faster feed) and standard groundbait feeder (slower feed) and obviously, of course, by how firmly you compress the liquidised bread in the feeder.
On waters like the Ribble, where the chub are used to feeding on pellets, I supplement the liquidised bread with micro pellets, some at the time of making the mash so it's well soaked in, and continually with a few pinches of micro pellets while I fish so they always have a few fresh and still crunchy ones. I never use anything bigger than micro pellets when bread fishing as I don't want to trigger the chub into feeding on pellets.
Using one of those Drennan flat bread punches can make a big difference when the chub are being tricky. And they make ideal samples for the feeder for they have already compressed about 40% of the punched bread.