Why does URLLoader.bytesTotal return a different value if the file is online or local?

I've got an xml file in my AIR app and I'm trying to determine his size. Here's what I did (seems complex so I don't know if it's the good way to do it) :

function checking_version_of_horairesXML():void{  
var url_local:URLRequest = new URLRequest("horaires3.xml"); 
var url_online:URLRequest = new URLRequest("http://www.mywebsite.nc/horaires3.xml");   

// Define the URLLoader. 
var loader_local:URLLoader = new URLLoader(); 
loader_local.load(url_local); 
 
var loader_online:URLLoader = new URLLoader(); 
loader_online.load(url_online);  

// Listen for when the file has finished loadingl
oader_local_Complete loader_local.addEventListener(Event.COMPLETE, loader_local_Complete); 
loader_online.addEventListener(Event.COMPLETE, loader_online_Complete);   

function loader_local_Complete(e:Event):void {  
trace("size of local file : " + (URLLoader(e.target).bytesTotal)); 
}  

function loader_online_Complete(e:Event):void {  t
race("size of online file : " + (URLLoader(e.target).bytesTotal));  
}

It seems that the code for the local file is working as I'm getting in output :

size of local file: 703693

But I've uploaded the exact same file on my server and I have this in output :

size of online file : 60243

Why am I getting different results as these 2 files are identical ?