Amp volume

Hi,

I am relatively new to amplified harp. I have a small (8W) tube amp and a large (55/60W) tube amp and whatever settings I use I still seem to get more volume out of the small amp before feedback kicks in. Am I missing something? Will the bigger amp become less prone to feedbaack with use or maybe my technique needs to improve? I've also tried standing in different positions in relation to the amp.