Correct me if I’m wrong (seriously) but I don’t think viscosity matters for most in vitro testing. In vitro something is often applied and measured, measured, measured, right? But in vivo, as with the dogs, viscosity determines “wear time”, right?
I imagine the thicker the dimethicone, the better the wear time and thus, better effect. Then it would come down to application and tolerability. A liquid isn’t going to be as substantial as a viscous liquid and a viscous liquid isn’t going to be as substantial as a gum. Then there’s the question of additives.
Ive seen as little as 0.5% dimethicone be listed as “protectant”. I don’t know if this has an occlusive effect. I imagine any amount will reduce moisture loss but to maximize this effect you probably need 2% or more, but I’m typically heavy handed with these types of things.