I cast False Life on myself, rolling a (d10+level) total of 10. I get 10 temporary hit points.
I am then wounded and lose 5 of those temporary hit points.
I cast False Life again, rolling a total of 6.
How many temporary hit points do I have now?
If you think the answer is eleven, you are wrong. Once you realise why you are wrong, you will understand why I am confused as to whether the answer is actually five or six!
The relevant section of the SRD is entitled "Same Effect More than Once in Different Strengths:"
The first casting was more powerful than the second, so does it make the second casting irrelevant: which spell is "best", the one that has the best roll or the one that is currently having the best effect?