I am awaiting a funding decision for an F award myself...My understanding is that all NIH grant percentile scores are calculated based on the study section reviewing the grant, not the award type, so while an application scoring at a lower percentile obviously has a better chance of being funded, nothing is guaranteed. There is a difference between an F30/F31 application percentile score being below the institute-published payline and the percentile score being below the overall F30/F31 success rate. There are also factors beyond "scientific merit" that affect funding decisions (like whether a "less meritorious" application fits an institute's mission better than a "more meritorious" application). A phrase that seems to be commonly thrown around in this context is to be "cautiously optimistic" if your percentile score is good.
The PO is probably the best source of information about one's chances, regardless.