the 1/2 zip is a little roomy but I think it works (like a windshirt). I wear XL in outerwear and Large in the regular fit polos. It's not overly big and sloppy so don't worry about that.
The merino wool v-necks (l/s and vests) are snugger and fit excellent! Just picked up the heather blue l/s and have another vest coming soon! Excellent stuff!