I think the big fish were wary of your fly because, well, that's how they got to be big fish.
All good suggestions above, but in my experience largemouths are not particularly leader shy. I usually start with about an 8ft leader, usually 1X or even 0X, and will fish it down to 7ft before I consider re-adding tippet. Now smallmouths are another matter, but you mentioned only bucketmouths.
Your issue may be more the clear water spookiness, as folks have suggested here, or very likely the time of day. These summer days, if it isn't early or late in the day, they're probably just looking.
And I tend to either fish the top or bounce the bottom; seldom in between. But that's just me.
And Frank's point about annoynce is very true. Fishing trout and largemouths are completely different. Drop a fly on a trout's head and he's gone. Drop one on a largemouth and he's lible to hit it out of sheer meanness. When it comes to threat reactions, trout are flight, bass are fight. It's part of their charm..