As long as the lowers can dance around inside a circle the size of US Silver dollar, you're good. Depending on your thread/toggle thread count: we use 3:2 ratio for each step up in wind condition. From a base of 16, we tighten the uppers/lowers 3:2 full turns, or increments of such: 3:2, 6:4...
Ullman? Good lord I've NEVER seen a set on a Melges 24. Maybe a rare bird on the Left coast. The only two names in Melges 24 class are North and Quantum. Look at any startline photo and pick out a single Ullman. The simple answer is 16 on the uppers and loose on the lowers.