Tangzhong/water roux method questions..

so I read about this Tangzhong or water roux method where u first cook 1 part flour 5 part water to a paste n cold before use.. So my question here is ..can I use this in any of my current existing recipe ?

for example a certain recipe of mine uses

1300g flour

710 ml water

..so if I wanna use Tangzhong method in this recipe 

is it possible to just 

Take out like 100 gm from the 1300.=remainder 1200

and 500ml from the 710=remainder 210

cook that part into a paste and use the whole thing back into your 

1200g flour

210 water? From what I read maybe extra water if too dry?

is this a proper or decent way to add water roux method to all my current recipe?

or is there a better method? like continue using the same recipe 1300g 710 ml but add extra Tangzhong? If that's the case how much Tangzhong do I even add ? Is there a ratio for that..

so which is it or neither ...haha

t in adavance