clarify replacing transactions (#959)

* clarify replacing EIP1559 transactions

Signed-off-by: Alexandra Tran <[email protected]>

* remove blank line

Signed-off-by: Alexandra Tran <[email protected]>

* fix list style

Signed-off-by: Alexandra Tran <[email protected]>

Author: alexandratran

docs/Concepts/Transactions/Transaction-Pool.md

@@ -39,10 +39,24 @@ transactions.
 
 ## Replacing transactions with the same sender and nonce
 
-For transactions received with the same sender and nonce as a pending transaction but a gas
-price higher than the existing gas price by the percentage specified by [`--tx-pool-price-bump`](../../Reference/CLI/CLI-Syntax.md#tx-pool-price-bump),
-Besu replaces the pending transaction with the new one with the higher gas price. The default value for
-[`--tx-pool-price-bump`](../../Reference/CLI/CLI-Syntax.md#tx-pool-price-bump) is 10%.
+You can replace a pending transaction with a transaction that has the same sender and nonce but a higher gas price.
+
+If sending a [legacy transaction](Transaction-Types.md#frontier-transactions), the old transaction is replaced if the
+new transaction has a gas price higher than the existing gas price by the percentage specified by
+[`--tx-pool-price-bump`](../../Reference/CLI/CLI-Syntax.md#tx-pool-price-bump).
+
+If sending an [`EIP1559` transaction](Transaction-Types.md#eip1559-transactions), the old transaction is replaced if
+one of the following is true:
+
+* The new transaction's effective gas price is higher than the existing gas price by the percentage specified by
+  [`--tx-pool-price-bump`](../../Reference/CLI/CLI-Syntax.md#tx-pool-price-bump) AND the new effective priority fee is
+  greater than or equal to the existing priority fee.
+  
+* The new transaction's effective gas price is the equal to the existing gas price AND the new effective priority fee is
+  higher than the existing priority fee by the percentage specified by
+  [`--tx-pool-price-bump`](../../Reference/CLI/CLI-Syntax.md#tx-pool-price-bump).
+
+The default value for [`--tx-pool-price-bump`](../../Reference/CLI/CLI-Syntax.md#tx-pool-price-bump) is 10%.
 
 ## Size of the transaction pool