For sub-surface stillwater fishing, you regain a lot of sensitivity to subtle strikes..which occur often on the retrieve pause...by keeping your rod tip near or slightly under the lake surface....regardless of leader length. A rod held up-right doesn't transmit low energy input all that efficiently. It adds too much slack to the line. In very clear water, in full daylight, a long leader can be critical...not so much in more turbid or poorly lit conditions. As for a tapered leader...a suitably stiff straight fluorocarbon line works just fine...all it really needs to do is deliver the wetfly without a big nasty tangle or splash. Yes, you're not setting a dryfly, and the strikes occur during the retrieve, but there's no point in spooking everything at the end of your tackle system.