iOS和Android Max BLE通告和扫描字节

I have been searching through stackoverflow; however, I seem to have found various conflicting answer's to questions regarding this. Given Android 5.1.1 and iOS 8.4.1 what is the maximum amount of bytes that can be sent through a connectionless BLE service to one another. It is my base understanding that it should be 20 bytes from BLE Specficiation(actually 23); however, I have seen queries where iOS was able to push 512 and android was able to increase it's MTU. I have been searching through stackoverflow; ho