This is no longer the case. Back in 2018 AWS changed the pricing model so now there's no more bidding.

This means "bidding" more won't protect your capacity, AWS will just take it if they need it.

Prices are now relatively flat, and changing slightly over time by a fraction of a cent per day with a cap at the OnDemand price, while previously there used to be lots of from 0.1x to 10x the on demand price and with swings even multiple times within a day.