Warning: Identity file $keyfilepath not accessible: No such file or directory.

Again, it looks as if you where quoting too much or using the wrong set of quotes (single instead of double, or qw)... Ummm, I guess you are passing $keyfilepath as follows:

$sftp = Net::SFTP::Foreign->new(...
                                more => [qw(-i $keyfilepath)],
                                ...);
[download]

Instead, it should be...

$sftp = Net::SFTP::Foreign->new(...
                                more => ['-i', $keyfilepath],
                                ...);
[download]

It is probably working anyway because you have the private key in the standard place ~/.ssh/id_*