They are too tall and the side zip should be on the outside. You pull them up so the elastic is against the bottom of your boot next to the heel. They do stretch out so if leather they should be snug but not tight to start and they relax a bit as you wear them. They should fit where the top of your tall boot fits. They will not relax around the ankle in the same manner a boot does so you are not fitting with that in mind. Wearing the zip on the inside will wear or marr the leather of your saddle. If you have matched the color to the boots they are going over they should from a distance look like you are wearing tall boots.
Some horse people change their horse, they change their tack and discipline, they change their instructor; they never change themselves.