Well , first i might have been a bit rude sor sorry about that .
Of course it's not a "magic" number coming from nowhere , it's the result of many test i've done on personal project over networking and other result shared by other dev on some forum in the subject .
It seems like this value (of 140ms ) is an average theorical value estimated after sending packets to a server (at a specific distance from the sending source ) and then analyzing each step done through the TCP protocol to ensure that data is not corrupted (this sentence doesn't make a lot of sense but from french to english it's difficult for me to be really precise ) .. and it appear that in average the server will take 140ms to process , analyze and check a packets of 64ko (i know we normaly use the kb unit ) .. on top of that it happen very often that packets can be interpreted as corrupted when they aren't and if not configured properly some data that normaly should be send individually , will be send as a group to meet the "12, 28, 32, 48 or 64ko weight per packet" requirement ... yeah i know it's kinda stupid but it happen .. and since the way ironsight seems to respond to user input (shoot , moving etc ) it can lead to some confusion about how the TCP protocol is used and if it's actually the right choice to make at the beginning ..
Of course just going for UDP will not make the game suddenly super playable , but maybe in correlation with a proper use of lag compensation (look very arbitrary at the moment ) it can make a big difference ... or absolutely not ..
Because if the server himself is not configured to handle smaller paquets or very important technical point well .. in this case there is nothing to do about it
As a conclusion i thank you for keeping your calm and still be polite in answer to my quite rude comment !