for my $chr (160 .. 255) {
    my $chr_byte = chr($chr);
    my $chr_utf8 = chr($chr); utf8::upgrade($chr_utf8);
    my $rx = qr{$chr_byte|X}i;
    print $chr . " " . ($chr_utf8 =~ $rx ? "ok" : "not ok") . "\n";
}

##</code><code>##

for my $chr (160 .. 255) {
    my $chr_byte = chr($chr);
    my $chr_utf8 = chr($chr); utf8::upgrade($chr_utf8);
    my $rx = qr{uci$chr_byte|uci};
    my $s  =   "uci$chr_utf8";
    print $chr . " " . ($s =~ $rx ? "ok" : "not ok") . "\n";
}

##</code><code>##

   ...
   my $rx = qr{uci$chr_byte|uci_};
   ...