Quote from: Robot1982 on November 01, 2019, 01:55:16 PM

-snip- This may still work if you only slightly increase the fee for the second transaction but still you cannot be sure that this transaction will be confirmed first.

Don't you worry, Electrum implemented RBF with accordance to the rules (wiki) otherwise, RBF transactions won't be accepted by the server (nodes) to begin with.
(except in some cases: bug)

Without clicking the link, #2 in the list indicates that the replacement transaction should pay additional fee of at least the minimum tx fee based from its 1sat/B fee rate,
ex: If the new RBF tx is 295bytes, then it must pay at least 295sat higher than the original tx; same with batching, but the minimum additional fee will be based from the batched tx.

TL;DR: You'll never be able to create a replacement TX with lower fees as it will be rejected by nodes.