I recently was trying to place a diagonal reverse calendar on SPX. For 10 contracts 1960 Put (Short) August Expiration and 1975 July( long) expiration, TOS platform online indicated $296K in margin requirements!!. I spoke to TOS and I was told that they charge 20% as the margin for naked options. I recall SPAN margin requirements was something like 10K for the same. Any thoughts or ideas? Appreciate the inputs from the members.