We double all distances. Movement, range, map size etc. Keeps the game dynamic.
Playing with 28mm minis using the 15mm table size and ranges just doesn't look right to me. But this is a purely personal observation.
When I have played FoF expanding the table size but using the standard ranges using 28mm minis, it seemed too slow.
Finally, I am limited to a maximum 4x6 table size, so we need to modify the maps for some secanarios. Frequently the scenarios are used to inspire our own, rather than playing them out exactly as described in the books.
We (our gaming group) have been very happy with our 28mm Force on Force games doubling all ranges, etc.