I used same strategy for ECN and non ECN broker and there is big difference if I use this parameter.
I there some error in values used?
There are two important settings - Spread and Commission.
The ECN brokers (by definition) have to provide the best prices from the Liquidity Providers they use and to charge the traders with a commission. However, most of the brokers sets the commission in the prices lifting the real spread (Lowest LP Ask - Higher LP Bid). As a result, there is no difference for the traders.
No matter how the brokers defined his policy, the true effect for the traders is the spread and the commission they charge.
Other effects come from the MT plugins and settings they use. It reflects on the market dynamic and the slippage. As you know, for example FXCM was found guilty for slippage manipulations. Be sure they are not the only broker trying to steal from his traders.
Do I have to change ECN spread parameter inside Monte Carlo Options to a smaller value for ECN broker?
See what is their spreads for your type of account and set a little higher value in FSB, no matter if the broker calls himself ECN or something other.
The ECN license is much cheaper (more than two times) than the Market Maker license, so many brokers has an ECN license. However, MT is designed to provide various manipulations for the brokers and despite the ECN license, they do what they want.