Question about vowel harmony

Hello guys!

I have strong interest in Hungarian language but it's more of a hobby than needing to learn it and speak it.

Basically, I'm trying to analyze languages and borrow their features to build my own "constructed language".

Therefore, I would like to understand a bit better the Hungarian vowel harmony.

I have read the superb work on the website hungarianreference.com, but I still struggle to understand how you choose between a short or a long vowel, when branching a suffix or Hungarian-izing borrowed words.

I've read a lot of hungarian song lyrics and I can't seem to find any regularity, sometimes I see words with the long vowel in the root, sometimes the long vowel in the suffix, or even vowels losing their length in contact with other syllables.

Thanks a lot!

Edit: just found another hugarianreference article that may answer my question 🤔 "Endings and lengthening vowels". Ah. Wish I found it before posting.