If I followed you correctly - the two side borders match?
And the top wnd bottom borders are off by an inch?
I think I would make the borders match (be the same size) - so they look the same -
then distribute extra length evenly - and then ease itt in.
I think most people would not notice a half inch of extra fabric distributed over a 36 inch or longer span.
One of the things I do when I'm attaching borders to blocks: if my blocks are all supposed to be finished at 12 inches and my sashings are supposed to finish at two inches - I mark those intervals on the border before attaching l also give myself some extra length on lthe border length - it's easier to trim off 1/2 inch than to be short that amount.
marking the border pieces before attaching them has sometimes alerted me to the fact that my blocks arent always as consistenttly sized as i thought they were.it also let's me know where I might need to do a bit of easing/stretching to give the illusion of consistency.