I have the LEAF Cold WX Zip-Neck AR and the LEAF Cold WX Long-Sleeve Shirt. They’re both great. They’re both thinner, merino wool base layers that are more about moisture management than straight insulation and warmth. But they perform great in cold weather.
If you’re gonna be static in cold weather, I’d recommend the LEAF Cold WX Zip-Neck SV. It should provide more insulation to you.
As far as the length, I’ve had no issues. I wear the Long-Sleeve under my armor and gun belt at work with no issues of it coming untucked.