I often see chances for the application of iriminage, but he is too tall to successfully implement the technique. Humor me, if you will, with your suggestions as to which technique would be appropriate in this situation.
No, he is not too tall.Your iriminage is not good enough - surely mine isn't either
If you cannot imbalance him, the only way is to try with pain - not necessarily a good idea, when sparring with a friend. You might try (next to gedan ate) kotegaeshi or nikyo.
Maybe it is wise to aask your sensei, how to apply iriminage or a simple ikkyo on tall, well-centered uke