Seatpost tubing thickness (in general)

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I've had no replies to my specific question on ITM posts so here's a more
general one:

For the same models, do manufacturers generally use the same thickness
tubing for their smaller sizes of seatposts as they do in the larger
sizes?

Thanks for any info.

I've previously suggested that the ITM Big One and Millenium seatposts
were the same things except for finish, but I'm not so sure now after
buying a 27.0 Millenium. The tube wall is much thinner than the 25.0 Big
One's so I'm wondering if different alloys are used after all. Millenium
= 7075.
ITM told me the alloys were the same (despite their website vaguely
implying otherwise) but I now suspect I was given duff info. Or could the
Big One use the same alloy but just more of it!?
Saddle clamp material is different anyway: same design but Millenium's
is slightly lighter stuff.

~PB