My shortest leaders are usually no less than 6'.
Short leaders (3 feet or less) are good when fishing sink-tip in moving water as it ensures the fly gets into the strike zone quickly and does not ride up in the water column effectively cancelling the effect of the sinking tip. In still water this is not as necessary as the need for the fly to sink quickly is not as important, furthermore the still water also gives the fish a better look at the fly, leader and line, so longer leaders used so as not to spook the fish with the more visible fly line.
None of this should have any effect on the ability to set the hook. More likely your fly is being hit by smaller fish who cannot (or are not) taking the fly but are merely bumping it. This can be solved by using smaller hooks (if you really want to hook these smaller fish).
Now, I am not sure why you have better luck fishing from shore, but I might suggest just fishing from shore then.
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