Let's say I want to sell covered calls on ES using SPX calls instead of ES calls. When selling covered calls on a stock it's easy to figure out the amount of hedge i.e when buying 100 shares of a stock you'd need to sell 1 call against it. Let's say I want to buy 100 ES @1140 and sell SPX April 1150 Calls. I dont want to use ES calls due to their low liquidity and also I'd like to use SPX options because they have European style of exercising(not called till the expiration date). The question is how many SPX calls do I need to sell against 100 ES to fully cover my position. The first thing that comes to mind is to sell 100 SPX also, but I am not too sure. Any help would be greatly appreciated.