any use in a lower dose of flea stuff?

I ordered 4 months worth of the over 55 lbs advantix and Petco sent me 6 months of the 21 to 55 dose. Sending it back seems like a giant pain in the ass. Should I just suck it up and send it back? Duncan is 90 lbs :/

I can't answer this question, however I ordered a year of 21-55 and I use it on my 45lb dog and my 60lb dog with no issues.

But I always wonder because I used to get the Over 55 for my 60lb dog and my 140lb dog and it worked equally good on both of them. That's a huge weight gap.