Actually even though you have a fitted baselayer already, loose is better for all layers. Fitted works fine, loose is just better, it tends to ride and bunch less. Not trying to offer useless advice that you did not ask for, but I find myself purchasing baselayers when I find them for a good sale whenever, so when you maybe add some more to your collection, try some loose.
When you get into the best baselayers ie, anything merino wool or like patigonia capilene 1 or 2, just doesn't have that hard stretch to it, but will give you the most lightweight/warmth/wicking you can imagine.
Same rules apply for all layers, just get a "loose" midlayer.
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