0.5 KB! 500kb is half a block.
It's just an estimator and of course it does, imagine somebody is dumping half a block of tx with 300sat/vb, if you keep your acceleration fees at 100sat/vb you're losing money by including that!
Also that fee on mempool is quite tricky, you need to read the thing carefully:
Nope, miners get screwed twice with accelerators
- they include free tx with lower fee, so lower income for miners
- they keep all the paid accelerators fees for themselves, while we get the initial fee for that tx that underpaid for that block space