The answer is simple.
Miners always try to maximize their profit.
a) The block can be filled 50% with tx at 2sat/vb, the next tx in order at 1.99sat/vb will cover another 30% of the space but the next two one each at 1.98sat/vb are 25% so they would either both fit or not, higher revenue for miners or fee order?
They will include one of the transactions paying 1.98 sat/vbyte and a transaction with lower fee rate to fill the block as much as much possible and maximize their profit.