In English, “long,” “short,” and “double” have special meanings. A double consonant is written with two letters, but is not pronounced and differently, and long vowels are not longer versions of short vowels. They are completely different vowels or diphthongs.

vowel: long – short
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a: mate – ah
e: mete – met
i: bite – bit
o: mote – bot
u: lute – mutt

So you’d have:

hoping (long) vs. hopping (short)
diner (long vs. dinner (short)

So hipaa would tend to be pronounce “HIGH-pah,” and hippaa would be “HIP-pah.”

In the real world, something gets traction and that’s how it’s pronounced. I can’t speak to HIPAA and how people who have to say it everyday pronounce it.