It's not so much "precisely" as "not ridiculously wrong". The difference between "slightly big" and "tent" isn't much, considering there is practically no objective basis to kids' sizings, which are basically the intended age with no consideration of variations in age & growth; the sizes do not reflect an actual size.
Yes, this! Just to get close to fitting, we have to get our son pants for a 6yo, shirts for a 4yo, and socks for a 3yo, and even then we end up rolling the sleeves on his shirts because he needs the length in the chest but not as much the arms. I can't tell you how many pants, shirts, socks, etc. we went through before figuring out this is the combination that works. Oh, yeah, and this is only with the specific combination of pant/shirt/sock brands that he's currently wearing. If we had to replace one part with a different brand (which we will, because he's growing and for some reason there's no brand that reliably stocks the full toddler-kid-youth size range), we'd be screwed.
