pronounceability algorithm

I am struggling to find/create an algorithm that can determine the pronounceability of random 5 letter combinations.

The closest thing I've found so far is from this 3 year old StackOverflow thread:

Measure the pronounceability of a word?

<?php
// Score: 1
echo pronounceability('namelet') . "\n";

// Score: 0.71428571428571
echo pronounceability('nameoic') . "\n";

function pronounceability($word) {
    static $vowels = array
        (
        'a',
        'e',
        'i',
        'o',
        'u',
        'y'
        );

    static $composites = array
        (
        'mm',
        'll',
        'th',
        'ing'
        );

    if (!is_string($word)) return false;

    // Remove non letters and put in lowercase
    $word = preg_replace('/[^a-z]/i', '', $word);
    $word = strtolower($word);

    // Special case
    if ($word == 'a') return 1;

    $len = strlen($word);

    // Let's not parse an empty string
    if ($len == 0) return 0;

    $score = 0;
    $pos = 0;

    while ($pos < $len) {
        // Check if is allowed composites
        foreach ($composites as $comp) {
                $complen = strlen($comp);

                if (($pos + $complen) < $len) {
                        $check = substr($word, $pos, $complen);

                        if ($check == $comp) {
                                $score += $complen;
                                $pos += $complen;
                                continue 2;
                        }
                }
        }

        // Is it a vowel? If so, check if previous wasn't a vowel too.
        if (in_array($word[$pos], $vowels)) {
                if (($pos - 1) >= 0 && !in_array($word[$pos - 1], $vowels)) {
                        $score += 1;
                        $pos += 1;
                        continue;
                }
        } else { // Not a vowel, check if next one is, or if is end of word
                if (($pos + 1) < $len && in_array($word[$pos + 1], $vowels)) {
                        $score += 2;
                        $pos += 2;
                        continue;
                } elseif (($pos + 1) == $len) {
                        $score += 1;
                        break;
                }
        }

        $pos += 1;
    }

    return $score / $len;
}
?>

... but it is far from perfect, giving some rather strange false positives:

Using this function, all of the following rate as pronounceable, (above 7/10)

• ZTEDA
• LLFDA
• MMGDA
• THHDA
• RTHDA
• XYHDA
• VQIDA

Can someone smarter than me tweek this algorithm perhaps so that:

• 'MM', 'LL', and 'TH' are only valid when followed or preceeded by a vowel?
• 3 or more consonants in a row is a no-no, (except when the first or last is an 'R' or 'L')
• any other refinements you can think of...

(I have done a fair amount of research/googling, and this seems to be the main pronounceability function that everyone has been referencing/using for the last 3 years, so I'm sure an updated, more refined version would be appreciated by the wider community, not just me!).