What you said is very misleading.

$ perl -le'
    $_ = "\xc2\xa0";
    print /^\h$/ ? "h" : "not h";
'
not h
[download]

Of course, you are referring to the internal encoding.

$ perl -le'
    $_ = "\xA0";

    utf8::downgrade $_;
    print /^\s$/ ? "s" : "not s";
    print /^\h$/ ? "h" : "not h";

    utf8::upgrade  $_;
    print /^\s$/ ? "s" : "not s";
    print /^\h$/ ? "h" : "not h";
'
not s
h
s
h
[download]

Unfortunately, that's irrelevant in the OP's case since he needs to decode his UTF-8 first, and will make the internal encoding UTF-8.