sub ratio_change {...}
my @args = ($start_value, $start_total, $new_value, $new_total);
ratio_change @args;   # Same result as:
ratio_change $start_value, $start_total, $new_value, $new_total;
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sub ratio_change ($$$$) {...}
my @args = ($start_value, $start_total, $new_value, $new_total);
ratio_change @args;   # Eeks. Won't do what you think it does.
ratio_change $start_value, $start_total, $new_value, $new_total;
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I don't shy away totally from using prototypes, but the only types I use are:

sub foo ();
sub foo ($);
sub foo (&@);
sub foo (\@@);
sub foo (\%@);
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I hadn't considered that argument, but it makes a lot of sense.  I can see where passing @list would now be prohibited because of a narrowing of definition of what passed parameters are legal.

Since I still prefer to put subroutines at the end of the file, and call them with the simpler my $result = function $a, $b, $c; (or my $result = function @abc_list;), I will try to stick to using prototypes like:  sub ratio_change; where the argument list (and parens) are unspecified.

There's no prototype in:

    sub ration_change;
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That's a (forward) declaration. If you use a prototype, both the declaration, and the definition of the subroutine should have prototypes, and the prototypes should be identical.
Perl --((8:>*