By this same logic
though if home fuel cost is $4.00 and you are away and pay $3.80 you should
still be reimbursed for $4.00.

This is correct. It's like an owner, who gets a bargain at $3.80 and a
bummer at $4.50.

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.