with all due respect... i question your methodology.
first, you estimated distance is precisely that: an estimate. it can be anywhere within +/- 20%, if you are lucky..
second, you are not sure how much fuel you used..
third, the tagaytay trip involves a slope. i am not sure the mileages involving this segment, are a true rendition of your fuel efficiency. i am not sure if it is safe to assume their (dis)advantages cancel out each other. and this involves more than 50% of your studied estimated distance.
my suggestion: have your odometer fixed. anything less than that, and your figures are immediately questionable. and involve longer distances over longer periods of time.