FOC will increase slightly by shortening the arrow. For instance an arrow that is 27" long will have a higher FOC with the same tip as the same arrow that is 32" long. Most people don't leave their arrows long enough to shorten, but if you did, then shorten it. A shorter arrow will act stiffer and can handle more weight on the tip. Adding weight to the insert will allow you to stay at the same spine and increase FOC a fair amount. This assumes that your spine was exactly what your setup needs to begin with.