you're definitely not missing something blindingling obvious.
If I use a slightly different example:
gyda often takes the contracted endings:
with me, him, her, you etc. are easy enough: gyda fi, fe, hi, chi etc.
with someone's brother for example:
gyda'i frawd - with his brother
gyda'i brawd - with her
gyda'ch brawd - with your
gyda'n brawd - with our
gyda'u brawd - with their
so, often all "ei" bits are dropped. If you don't drop it, you'll be absolutely fine and understood and grammatically correct too. So don't get bogged down by it