Alison
Hi,
I can't comment for Bravecto, except that I felt more comfortable using it given the fact that my 2 dogs are on the upper end of the weight range.
But the worming tablets I use have 2 options (sorry, have to use metric, I'm Australian????) - less than 5kg, and greater than 5kg (up to 25kg, before the instructions advise to give more than one tablet for dog's over 25kg). Now my 2 Cavoodles hover around 8.5kg-9kg, and when transitioning my eldest from the up to 5kg tablet to the next one...I did the math based on the numbers on the packet, and I couldn't possibly give her the bigger tablet - it was literally 6 times the therapeutic dose required! So I did 1.5tabs of the smaller one until she outgrew that, then I halved the big one's, and have been doing so ever since (same deal with her little sister) - so they're still both getting on average the required amount for a 12.5kg dog on 1/2 a tablet, why on earth would I give them 3 times the therapeutic dose by giving them a whole tablet!?!? What a stupid range to have! Giving a 6kg dog the same as a 25kg dog? Don't think so.
So I'm with you on narrowing the dose if your pet sits in the middle or on the lower side of the range!