A couple of quick things:
Cultures:
While both TA61 (what I use) and (your) YC-380 both contain Streptococcus thermophilus,
I add LH100 which contains:
• (LH) Lactobacillus helveticus
• (LBL) Lactobacillus lactis
The Lactobacillus helveticus does several things, to include the prevention of browning.
But you also add Lactobacillus delbrueckii subsp. Bulgaricus as this is included in your YC-380.
From what I understand, this is typically used in the production of yogurt. So, I’m not sure what that means to Parmesan.
Enzymes:
While this should not affect your curd production, I saw no mention of Lipase. To me, this gives the parmesan its distinctive "tang".. It’s hard to describe.
Rennet:
You mention that you used Renco Rennet, but did not provide any dosage information, or flocculation time. Both of these greatly affect curd production. I use a dosage of 9ml rennet to 100lbs milk, diluted to at 1:40. I also use a flocculation multiplier of 2X. That is I measure how much time for the curd to initially set, then wait that amount of time again before cutting the curd. This also affects your curd. The longer you wait, the more moisture is contained in the curd.
These are the things that jump out at me right away. There are other recipes in this section that show how others have fared. You might look at Marks’ parmesan posts as I know he has been all over parmesan lately.