In the case of carp, even when you see lots of them cruising round just under the surface, a ledgered bait can still work in my experience as there must be other fish on the bottom. Is this also true with roach?
There have been times when I have ledgered for roach, and caught other fish such as skimmers, but no roach. I've wondered 'is it because they are up in the water?' But you'd think that baiting up would bring them down to the bottom. But does it?
At close hand, of course, float may be a better option anyway, though personally I have a problem seeing a float beyond a couple of rod lengths away. I suppose the underlying question is 'Is ledgering for roach viable when water temperature is high?