Yes it would.....but before you add that 'splash' fill the tank with original recipe......its only meant as a guestimate anyway, so if my 4ml tanks are say half full then while being a guestimate it will put you closer to the ball park......That would require remembering how many mls you estimated was in the tank to begin with.
And please note that what you use has to be consistent to what you have measured your drops for 1ml to be. In other words, I always use the same type(1 specifically) of cap(topper) for my 30 ml bottles. I also have a really good idea(cause I measured) of how many drops equal 1ml. Learned a long time ago that you need to use the same type of measurement tools to be consistent in repeat type of recipes. Call me old school.....lol