If you have a 4x margin account with IB and have your algorithm set to utilize only 2x margin can you effectively use 2x your initial capital without an error?  My paper trade account doesn't seem to have the capacity for margin as my order was invalid after trying to use 1.1x account value.  I'm concerned this will happen in live trading as well despite the copious margin I've been provided. 

On the side, is my logic correct that I will never use the entire amount of margin provided by setting the algorithm to use a maximum margin amount of 2x when in reality I have 4x? (essentially I never want to use the entirety of the margin allowed, but do wish to utilize up to 2x under special cirumstances)

Thank you for your assistance.