Cant get image flush in module position

Hi

I`m trying to put an image in module position "adv_top" but its consistently getting resized much smaller.

its gets taken from 710x226 down to 645x206.

Is there something fundamental I`m missing here?

I've solved this now, thanks.

Want to post the solution so others can know too if they come across this . . . ?

I feel like an idiot, my browser was zoomed (i didnt realise!), so all my image calculations where wrong.