K9 Advantix doses

I am going to order some K9 Advantix and Athena is right at the dividing point between does 21-55 (she is 56lbs) so I am going to give her the lower dose. But Sal is 63lbs, I am leaning towards giving him the lower dose because I am a little worried about the next dose being good for dogs twice (or more) his size as the dose says 55lbs and up. Meaning that it would have a big enough dose for a 200lb Eng. Mastiff

Am I just over thinking this? If I give Sal the 22-55 dose will I be wasting my money?

i usually divde doses on the wowies with advantix so we get the 21-56, charlie gets half, ruby gets half of that and then the rest is divided between the wowies and jasper.
so far absolutly no issues doing it this way.
(and its cheaper)

I buy the big something to 55lb one. And divide it up between the two 20ish lb dogs, the 8 lber and the 5 lber.

So do you think it is better to slightly underdose?

when we divde up where the max dose charts in at they probbaly each get mildly overdosed.

i found dividing it doesnt work as effectivly with frontline though.

so id say advantix is probably a stronger diultion in order to take division of a tube without loosing effectivness.
if your worried id air on the side of caution, get the smaller does and keep an eye, if he picks anything up this time around try the higher dose next time.

or get the max dosage size and divide it between both dogs.

good advice thanks