It is more complicated than I completely understand , but the big one is moisture left in the curd before salting .
Much too much and you get slip skin , a little too much an it seems to me the curd is just more runny .
And this is mostly controlled with Flock multiplier , or at least that is where it starts, then how much of that moisture is removed before molding and during molding .
With my lactic acid set I control it with how I scoop it into molds, as there is no cutting ,stirring , heating .
I can not say for sure if final ph plays a roll or not , but .
My charouce is always bottomed out at ph 4.4 or so and yet the wet ones end up runny or even slip skin , and if I get them dry enough they are firm and will age out to a grating cheese instead of a runny mess.