I added 20% water to the amount of milk (14 liters) this time and it worked for me quite nice. Maybe if the fat content would be higher, I would add up to 30%. However I had ~4 kg cheese (fat, protein, water content) at the end, the smaller one's had 180g (20 pieces) and the 2 bigger one's had 240g. If I knew the protein and fat content exactly, I would calculate the exact water content to add with a mixing ratio calculation, based on the fat content (was not the case, because I had it from a sheep farmer nearby and he could not exactly tell me, because he normally delivers it to a creamery and they have not told him for this month).
Example with 100 liters:
• Milk (6% fat content)
• Water (0% fat)
• Target-fat-content: 4%
6-4 = 2 units water
4-0 = 4 units milk
6 fat-units in total, so 100 liter divided by 6 and multiplied with the units for milk and water (4 and 2)
Milk: (100/6) x 4 = 66,6 liters of sheep's milk
Water: (100/6) x 2 = 33,3 liters of water
So you have milk with 4% target-fat-content.
I hope I could help you with that.