Parthian/Sassanid heavy cavalry use bamboo lances?

[Koyuncu]

The term "couching" involves tucking the weapon under the arm so the attacker can use part of the horse's momentum in the attack. This is exactly what is occurring. How is the second hand relevant?

I have never encounter a two hand couched lance in any kind. There is however two hand usage of long lances. Also, in the plate, the character's elbow is away from his body indicating that lance is not tucked between arm and body of rider. Like this one;



There is no projecting part of lance. I think, Sassanian rider is holding the end of lance and trusting with both hands there.