Concentration Rate is indicated when applying the penalty rate and the penalty itself. Concentration Rate of 50% means that if position value x 50% exceeds the total Account Value, that position is then considered Concentrated, and the per cent of funds blocked for margin will increase from the normal leverage rate to the Concentration Rate value.
A client with an Account Value of 10,000 USD opens a position worth 12,000 USD. The position value x 75% is below his Account Value; therefore Leverage Rate of 20% applies, and 2,400 USD is blocked as a margin (12,000*20%).
A client with an Account Value of 10,000 USD opens a 25,000 USD position in RDS.B.NYSE. The position in RDS.B.NYSE x Concentration Rate Long is higher than Account Value (25,000x75%=18,750>10,000), therefore Leverage Rate of 75% applies, and 18,750 USD are blocked as a margin for this exact position.
Other positions will follow the same logic separately, the total margin will be the sum of individual margins (normal or penalised, depending on each individual position size and penalty rate).
Concentration Rates apply to the majority of Forex and stock/ETFs instruments. Concentration rates are also set for some futures and options underlyings. Leverage Rates, as well as Concentration Rates, are set by the Risk department on a case-by-case basis and can be changed at any time.
You can always check the Concentration rate in the Instrument Info module on your desktop platform.
Concentration margin is a global setting and cannot be deactivated for specific accounts.