Quote from Mr Subliminal:
I agree in principle with your schema, though you will find rational investors on either side of the spectrum. In answer to your question, nothing makes sense regarding margin requirements - whether it's $5,000 per contract or $25,000, none of us are immune from an event which wipes us out. With that in mind, I append my rules which are very similar to yours, except for the "tightening up" as the trading capital increases.
Maximum contract size (MCS) = Equity / 5000, rounded to lower integer for (Equity < $30,000).
MCS = 5 for ($30,000 <= Equity < $42,000).
MCS = Equity / 7000, rounded to lower integer for (Equity >= $42,000).
Maximum value of MCS is 10.
eg. for $18,000 account, MCS = 3.
This is based on the CME Current Initial Spec ES margin requirement of $3,563 - any future changes will result in proportional readjustment of the MCS parameters above.