What people who complain about 99LP don't realize
Every single person i've seen who complained over getting 99LP always suggests that adding a system where getting 95-100LP would fix it because you would no longer be 1LP away from 100, but here's the thing, if 95LP was all you needed to get into your promos, and say you ended up with 94LP, you would be in EXACTLY THE SAME PROBLEM AS BEFORE! Lowering the required amount of LP to get into your promo series won't prevent you from getting annoyed by being 1LP away from your promo series, i'll all just put you right back where you were when you first started.
If it were changed to requiring 95LP for a promo series, you'd then say that to fix 94LP, adding a system where getting 90-95LP would qualify you for a series, then after 90LP were required instead of 95LP, you'd suggest that to fix 89LP, adding a system to qualify you for a series automatically if you got 85-90LP would fix it, then after it's changed to 85LP, then 84LP becomes a problem, then 79, then 74, 69, 64, 59, 54, and so on.
See how it doesn't fix anything? You're trying to fix it by setting yourself up to be screwed over again, in the exact same way, all over again.
It's League's equivalent to the Unexpected Hanging parodox. https://en.wikipedia.org/wiki/Unexpected_hanging_paradox
At least when being 1LP away from a series, you can afford to lose 1 game and still be 1 win away from a series.
There probably is another way to deal with 99LP, likely using a % of LP gained in some way, but this "lowering the flat amount required" is definitely not one.
TL;DR: Lowering the flat amount of LP required for a promo series to fix 99LP doesn't work as it in no way fixes the possibility of you ending up 1LP away from your goal all over again.