I think all this talk about molecular weight is far less important than what people give it credit for (at least for overall absorption potential). In the lactoferrin study they talk about large molecular weight proteins (10+ kDa) easily making their way to the to the hair follicle via the hair shaft. They pretty much plopped a 80 kDa protein in nothing but water, smeared it onto mice backs and observed increased hair growth. Granted, it was mice, but I believe that large molecules can enter human skin with similar ease. Here it is (check references as well):
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6546667/
I think this is even better because rather than entering via the skin, entering via the hair shaft gives it a greater chance of binding to some part of the DP and staying there, rather than cruising around into the bloodstream. In fact it only makes me want to increase the size of other molecules by attaching some protein to them to make them less likely to cause side effects. However given my experience with fina I'm not going to be one trying this, but good luck to whomever does.