I had a Highlander with shoulder gussets which was true, almost generous on the sizing.
However, I have a couple of the cheaper Tempest rugs with no shoulder gusset and I do need to go up a size on those.
Interestingly, I love the Tempest because I find them nice and deep. Other makes of rug look like a mini skirt on Millie, as her body is the weirdest shape.
Shires tempest are my go to rug for her.
Find them pretty true to size and use them on three very different sizes/shapes of horse, agree that the Tempest is a bit tighter than the Highlander but I'd expect that of any straight cut vs shoulder gusset rug tbh
6ft6 Shires Tempest fits MrT better on the shoulders and has more depth than 6ft6 Weatherbeeta. 6ft6 Weatherbeeta is longer but I prefer the Shires fit. His 6ft6 Shires Highlander fly rug is very generous. If he actually needed a rug I'd splash out on a Highlander turnout. But as he can be naked most of the time I stick with the Tempests.
I have a shires rain sheet. I got the size he normal is and his bum hangs out it a bit so could have done with a size bigger but he does have a big bum
My two are in shires 6 3 size Tempest whic I like as they are very waterproof, cosy but don’t weigh much. However one has a 6 in an Irish brand rug i have which is a bit smaller but still fits him ok. So you might find you do have to go up a size if you are used to another make. Shires seems the same size as weather beta to me.
We've got a highlander. It's a 6 9 but could have done with a 7ft really. It got used all winter for the last 2 years and have just put it on this year and it's a good rug