Firstly, set $File::Fetch::DEBUG=1;.

Ideally, File::Fetch should have had a method to provide it with a user-created LWP object in order for the user to have full control over it. Diagonally looking at the source:

    ### set up the useragent object
    my $ua = LWP::UserAgent->new();
    $ua->timeout( $TIMEOUT ) if $TIMEOUT;
    $ua->agent( $USER_AGENT );
    $ua->from( $FROM_EMAIL );
[download]

It looks to me you are out of luck with File::Fetch if you want to fine-tune LWP. Though, LWP is not the only tool it uses to fetch files but it seems to me it creates them on the fly during each fetch() and with a minimal set of parameters decided by it.

In the past I have used URI::Fetch which optionally accepts a pre-cooked user-specified LWP object which you can tune to your heart's content:

my $ua = LWP::UserAgent->new(...);
URI::Fetch->fetch($uri, 'UserAgent' => $ua) };
[download]

FInally, LWP::UserAgent can be made super verbose (dumping the headers for example) with:

use LWP::UserAgent;
use LWP::ConsoleLogger::Easy qw/debug_ua/;
my $ua = LWP::UserAgent->new(...);
debug_ua($ua, 10);
[download]

bw, bliako