YOU SAID:

I am a high horse when it comes to getting high on a horse

INTO JAPANESE

馬に乗って高くなることになると、私は高い馬です

BACK INTO ENGLISH

When it comes to riding a horse and getting taller, I'm a tall horse

INTO JAPANESE

馬に乗って背が高くなるということになると、私は背の高い馬です

BACK INTO ENGLISH

When it comes to riding a horse and getting taller, I'm a tall horse