Castelli sizing?

Why is it that their size chart definitely puts me at medium yet medium seems to be too small? Im talking bibs and tights here. Are they meant to be almost painfully tight? I see that many seem to buy a size bigger than normal but this doesnt make sense. Do they stretch with use so end up fitting after a few wears?
Pegoretti
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Colnago
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Colnago
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Colnago
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It would be nice if they could at least be consistent.
Edit: all those are castelli Bib shorts or tights, so suggesting it would be nice if we could have consistency within a single manufacturer.
Even vests can be ridiculous in choosing best fit... Specialized bases need to be L and still they are tight .. yet Craft (better imo) are M for a good close fit and a good length.
I do like Castelli.. but yes even at 6' 1 shorts will be L but tight until on the bike and a summer jersey could get away with a M.. but my newer Gabba 2 for this coming winter season is a L and tight fitting enough to avoid the ultimate roadie nightmare of flappiness.
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yes, i did otherwise no way they'd fit
with castelli shorts/tights they seem to be based on a model with skinny thighs in proportion to waist size