Limit of totalMarginBalance

Hi
sorry if i am asking something that is explained somewhere, but i couldnt find it.
I am trying to anticipate the fact i will have enough margin to pass a trade, when close to liquidation.
i have found out that in the interface the Margin Ratio seems to be equal to totalMaintMargin/totalMarginBalance
could you confirm it please?
it seems that this ratio cannot be more than 50% could you explain why not 100%? please

thanks a lot

margin ratio = Maintenance Margin / Margin Balance

it can reaches 100%, then the position will be liquidated.

thanks a lot