To be fair, at current pricing, 40 contracts on ES would require only $198K to hold through the close. But still, it seems an excessive request of any firm. Why not try four contracts? That would require only $19.8K, and you have more than that and wouldn't need a prop firm.
The "Dollar value" of 40 contracts is $5Million. If the underlying moves against you by 1/2 of 1%, your $25K equity is wiped out. That would be about 12 points.