A little column A, a little column B. The problem isn't really the length of the molecules, but the carbon fluorine bonds in it. Those are what make them so stable and why this compound class is used at all.

Bigger molecules are not so easy to get through your cell membranes, which is why they argue that they are safer. Problem is, that over time they do kinda break down into smaller molecules. So over longer time frame they release unsafe molecules in small amounts.

Shorter fluorinated compounds are faster going into your cells but also out of them.

Then the question is how much damage do those compounds while in your body? That only time (and studies) will tell.

But honestly? After working on the analytical part of that field for a bit and seeing how the industry bullshitted their way through till now? I don't trust them one bit.