Joe, I posted in the other thread for how you know if you have too much or too little. You have to hit 5.4 between 4 and 5 hours from the point of adding culture. The amount of the starter you add has to coincide with that. If you add 1% and it takes, say, 6 hours to hit 5.4, then it's not enough. If you add 1% and you hit 5.4 in 3 hours, then even 1% is too much. The initial drop to 6.5 doesn't have a specific time target - it depends on your culture. If the pH curve of your culture is such that it is very slow to begin, say, a .2 drop is 2 hours, but then will do a .8-1.0 drop in the next hour, then you need to either use a different culture, or adjust your make. to hit the pH targets.
Your pH targets for cheddar should be ~6.1 (not below 6.0 at finish) at drain, and 5.4-5.45 at mill (depends how long it takes you to mill - no lower than 5.35 by the time you salt.
You use TA, so I think it's something like 0.2- 0.22 TA at drain, and .45-.55 at mill/salt.
Make sense? It's about the entire acidity curve, you have to hit the moisture targets at the same time as the acidity targets when you drain, and you have to hit the milling pH targets about 4 hours into the make.
My guidance above is for high-quality, 36% MFFB, 6+ months aged medium to sharp cheddar. If you're making other types, you can take the short cut and use a shorter make and hit 5.4 in 3-3.5 hours.