Thank you Markus, I will consider the AP-ANT-48 antenna as my 60º choice per AP-324, its radiation pattern looks like much better than the D607 pattern.
I think if antennas is mounted under the seats, people will break or steal them, this is why I want to mount under the concrete, but I have to do test before to take a decision.
The arena is the other problem because is used for bullfighting events, car exhibitions, music concerts... and is necesary to get good WiFi performance and a rude installation (I'm evaluating solutions like OBERON NEMA-4 enclosures mounted on the bullring wall).
Sure I'm going to ask here more questions and doubts, thanks for all answers.