I find plants growing in bright light to have smaller leaves and bigger pitchers than those grown in low light. I use this to get some green mass on seedlings fast before moving them to brighter light at an age when their pitchers should be more interesting. That said, I haven't been growing nepenthes long enough to say that this actually achieves anything beyond optimum use of my limited space.
I grow highlanders in my lowland conditions and obviously, this is extreme adaptation, so my observations aren't probably as valid as those growing them in only slightly warmer conditions, but my highlanders tend to shrink in warm conditions till they acclimatize with normal or smaller pitchers and grow normal leaves in low light and cool temperatures also without better pitchering. Light seems to be what they want for good pitchers regardless of temperature. I give my acclimatized highlanders bright light regardless of temperatures, even if it means they can go up 37C in peak direct sunlight (any hotter than that and I cave in and shade, but that is rare). Those that acclimatize appear to grow normally with growth slowing in warm conditions, but leaves not getting smaller. If the light is good, they will pitcher well unless crazy hot.
This also happens to the lowlanders, though less dramatically.
So for me, for better pitcher to leaf ratio = LIGHT
If it can be done without cooking the plant, excellent.
I also have found better pitchers with the orchid "bloom" fertilizers than the regular nigh nitrogen ones and now for my healthy growing nepenthes, I use the bloom fertilizer, while I use the high nitrogen one for seedlings that need to bulk up the green first.