In reality, neither of those are showing ,,real'' battery health percentage, although Apple's one is way more accurate than any other program. I suggest you to watch this 8 minute long video, where you will probably have more idea what battery percentage you have and how battery health works. Also, I wouldn't be concerned about BH and create unnecessary paranoia while using my device. It's part that is meant to be used, and over time degrade. I would be happy to see that 87% on iPhone 7 Plus, because my friend recently had to change his battery on iPhone 7 because his battery health dropped to 49% and it was not usable while not on charger, so you are doing really good with it.
https://www.youtube.com/watch?v=w6--6z4ZcNk