Well... just looked on the Frontline Plus webby site...

"THEY Say" to dump it all in one spot...
"To Apply FRONTLINE Plus.
Place applicator tip through animal's hair to the skin level between the shoulder blades. Squeeze applicator, applying entire contents in a single spot to the animal's skin."

Seems to me I member Doc's Gurl saying to kind of run a stripe down their back - but making sure it went on the SKIN and not on the hair.

Dunno... sounds like all in one spot should not have caused a problem.

Here's the Merial/Frontline web site:
Frontline by Merial