Most jods stretch.But they should not be tight behind the knee. Neither should long boots. Victorian gentemen used to suffer a known syndrme from restricted circulation caused by tight riding boots.
When you actually sit on a horse your thigh muscles may expand a bit (contract - short and thicker) and the slack is taken up, So try sitting astride a chair and see how it feels. You need to be able to relax your knees and feet and toes when riding.
If you ride Engish the tightness below the knee (or half chaps|) is to stop cloth or your skin catching in the English stirrup leathers. But it is fine to ride in Jeans and many men do so.