Most of Schleich's horses are not tack friendly. They just aren't, let's start with the more obvious issues.
When tack is on a real horse the mane and forelock go over the bridle and saddle, which is hard to do with plastic.
Models like this are not a good choice for performance for many reasons,
A) all the hair, You just don't find real horses with that much mane
B) the bridle won't fit, due to the fact that the mane is pressed into the throat, where the throatlatch would be, as with the forelock which is all over his forehead
C) the thick mane is flowing over his back would go under the saddle.
Let's have a look at some other horses
He has a nice clear space for most of his bridle, he does have a bit of forelock but this is not a huge issue. The issue this mould has is that his tail is braided and his mane is loose, Which as far as I can tell is not against rules but is just considered really sloppy.
This horse's forelock is back and mane his off her back however some of her braids go where the throat latch would go.
For English classes, this horse (and other braided models) is quite nice, her tack will be able to fit nicely and she is presented correctly for many classes.
What I am trying to get at here is that not every horse will be able to do well in performance but if you look at your horses you should be able to find someone who will work. It is also important to pay attention to breed, body type and gait (I am happy to write a post on it later if you guys would like)
The next thing I plan to write about is Tack fit, let me know if there is something you would like to learn about and I will do my best.