...ball FIRMLY on the powder is all that is necessary for optimum performance.
Something to note regarding marking your rod or putting a stop on it; as you continue to fire your rifle, especially on a small bore like a squirrel rifle, the fouling in the breech area/powder chamber, continues to increase little by little, diminishing the area where the new propellant can rest. This in effect, raises the mark on your rod a little at a time, until by the end of the day, say 60 rounds, your ramrod, though seated the same way as on the first shot, will show its mark above the level of the muzzle, perhaps by as much as 1/4" It would be a mistake to try to compress the charge just to get the rod down to the mark.
So while not ignoring the mark, use it as a quick reference to show that you are in the vicinity of seating your load. Providing you're not trying to load through a rough or heavily fowled bore, you'll know when the ball is on the powder.