Passive RFID design assistance
If you aim >= 30cm, you definitely need a 128kHz RFID system. 

But I doubt that you can read >= 50 tags with RFID at all, because with RFID, each passive tag needs to be powered from the reader. 

You might want to try BLE (bluetooth) technology. The latest versions (5.2?) of that standard supports angle detection of the devices.