How can I improve the reception of my coaxial collinear antenna (1090 MHz)?
If the antenna is located in your living room, then the incoming 1090 MHz signals will be blocked by your house. 1090MHz signals are more-or-less line of sight. They don't travel very far through concrete or wood and are severely attenuated by glass, especially is you have energy efficient windows. 

I suspect you have a window towards the East or South East so that you have some signal reception from that direction. Try to put the antenna outside, preferably on top of your house to improve your signal reception.