The network pays out rewards to your masternode public key. That means the rewards are in the wallet associated with your masternode.
If you move rewards, they are technically no longer rewards but rather inputs to a new transaction. If the Node40 monitor page shows that you have 10 Dash in rewards, but you then move those 10 Dash to create a new masternode, the monitor page will update to show 0 Dash in rewards. That is because the 10 Dash became a basis for your new masternode.
If you want to see the flow of Dash associated with your masternode, the monthly Portfolio Insight Reports display details of every single transaction.