Line diameter plays a part for sure. But some floros are more limp than others, and those are what you want. You typically get what you pay for with Floro so just try some until you find what you like. Also you typically want to use the smallest weight you can get away with and still feel what you're doing, again for the most natural movement.
As far as the situation you presented where fish are in 40 ft over 80, that is definitely a challenging scenario. It will test your boat control skills just as much as your fishing skills, and you still may not get a bite. These fish are notoriously finicky. As Quillback said, I'd prefer to find fish relating to the bottom more. In my opinion you utilize more of the dropshots capabilities this way. Once the weight is on the bottom and you give slack the bait with flutter/glide/fall down nearly weightlessly. Essentially you can mimic the fish-catching qualities of a senko/slow fall lure but you can do it on the bottom in deep water. Anyway, sometimes if that 80 ft is next to a break/drop, you can follow it up and you will see that there are fish on the break relating to bottom at a similar depth that the suspended fish are out over the basin. In this example the fish are on a deep break relating to 35-40 ft just like the suspended fish over 80.
From my drop shotting experience as well as ice fishing experience, you almost never want to drop directly into the school you see on your graph. The fish are looking up in this scenario so that is where you want your bait to be in relation to the fish. If you can get them to rise a ways to eat your bait you can get those fish to bite something IMO. May not be the color or lure you have on right now but its probably close if they came up to take a peek. If you can get one to commit the next couple should be easier as it gets them more riled up similar to how one might get a school fired up on the ledges on Pickwick. I think what everyone said about not giving too much action is spot on. In my simple way of thinking here is what I envision: if there is bait involved, all of the bait is moving freely and naturally swimming around, so when you drop your dropshot in there and it has a duller/slower action this presents itself as a weak/dying/injured baitfish. Not to say you wont catch any shaking the crap out of it cause both have their place. No different than sometimes they want the jerkbait/topwater paused longer or worked faster, its not my place to tell the fish what they want.
Got a little wordy there, hope something in there is helpful.