No matter what equity you start with at C2, the trades that are placed in your model account at C2 will be the exact same quantity that you place at IB (for example).
In other words, if you trade 5 at IB, you will trade 5 at C2.
It doesn't matter if your C2 Account is much bigger or much smaller than at IB.
So the main thing you need to do is make sure that the account size at C2 is big enough to support whatever quantities you trade at IB.
There's no need to make the account sizes EXACT.