“be reasonable, by base layer I think we all mean close fitting”
I don’t – I mean the next-to-skin layer that manages sweat. For hotter conditions you don’t want it to be as close fitting or you want it to laterally wick to maximise evaporative cooling, for cold conditions it’s more important for it to rapidly wick away from the skin so a closer fit is preferable. If I’m not wearing a pack and it’s hot I’ve reverted to cotton T-shirts as they’re better at keeping you cool.
“I wear a jersey”
Whenever I’ve tried things like cycling jerseys they’re always too damned hot, hence I go for one or two base layers (one short-sleeved, one long). I do wonder if I’m missing something though?