Magpie Model Horses are generally considered 1:12 scale, which means 1 inch in miniature scale equals 12 inches in real world scale... ideally. In the model horse and the dollhouse worlds, 1:12 scale often covers a bit of a range.
The horses below are all considered 1:12 scale models, but you can see what a difference there is not just in height, but in the scale of the sculptures.
There is even a certain amount of inconsistency in scale between
individuals within their own brand. I'm not saying this as criticism, I
am an avid collector of all of these models, but just to illustrate how
loosely we throw about the 1:12 scale label.
Julips, by nature of their materials are on a slightly more massive scale as their legs cannot be too fine as it causes production difficulties due to their leg wires and overall weight of their bodies, and the latex tends to give the sculptures a soft, pony-ish look. Plastic models have more leeway in this area as they do not flex and are made of a lighter material. So a Julip model of the same general size and even breed type can look like a larger scale pony rather than a smaller scale sport or light breed.