Thank you for the guide!
A strategy guide book is recently published in Japan, it contains all formulas and other stuff in FETH. Unfortunately I don't have it, but there is a screenshot on how exp system works (based on my limited Japanese and google translate), and it looks similar to what you found so far.
(rough translation)
kill exp = (enemy type base exp) * (enemy level coefficient) * (coefficient of level diff in different difficulties) * 2 (for bosses and demons)
dmg exp = 1/2* kill exp * dmg percentage
The healing part has an extra part based on your description. It adds an extra penalty based on # of turns you've taken so far. So under 20 turns it is 100% and then the coefficient decreases slowly.
I'm not sure if the book is edited by the developer. Clearly there are some typos (missing %, missing numbers). You can find the book on amazon jp: https://www.amazon.co.jp/ファイアーエムブレム-風花雪月-パーフェクトガイド-ファミ通書籍編集部/dp/4047334294