The problem was that prices for the put at the 3,100 strike was fairly low when I opened it in June. Now, those puts value has risen by 50 % and next months expiration is even more expensive.
My strategy is focusing on getting protection for about 100 Euro. For that price I could only buy puts at 2,700 points which is by far too low based on my actual break even points around 3,100.
That's why I decided to add extra protection using bear put spreads. So I bought more Puts at 3,000 points and sold the complimentary amount at 2,900 points. In worst case they will pay almost 1,600 EUR and cover some of the losses.
Based on my current position with two open straddles at 3,350 and 3,550 I was supposed to buy two long puts. In fact, I sold my July protection for a profit at 151 EUR. For August I added two long puts at 2,700 for total cost of -194 EUR after commissions. For extra downside protection I bought two bear put spreads for a debit of 538 EUR - 822 EUR = -284 EUR after commissions.
All in all I paid 327 EUR for August protection.
I am planning to close the bear put spreads if EuroStoxx50 rises above 3,450 points. But that depends on the general market conditions after July 17.
