Well, the only way I can suggest is that the first finish experiment is a 'throw away' experiment done with a very small quantity of emulsion.

Also, the fogged emulsion can still be chilled and used to give you an example of what the speed is, albeit a foggy speed. Then too, remember that quite a bit of reflection fog does not show up when coating on film, so when you first see it on a blotter (reflection) then it will not be visible on film (usually depending on level).

So, two things to remember here. First, the initial attempt is a throw away but you can use it for generic tests. Second, if you catch it in time, the finish will not work on paper, but will work on film most of the time.