iOS: RestKit loadObject & send params

Question

using loadObjectAtResourcePath on GET method, doesn't include my parameters on the requests.

for example, if I send:

[RKObjectManager objectManagerWithBaseURL:@"http://something/ws"];
    [[RKObjectManager sharedManager] loadObjectsAtResourcePath:@"/res" delegate:self block:^(RKObjectLoader *loader) {
        NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:
                              @"val", @"param1",
                              nil];
        loader.params = [RKParams paramsWithDictionary:dict];
    }];

the final url request doesn't include the "?param1=val" part - why?