2 of 4 added 372 characters in body

Only a few miles....only a few feet... etc are not durational measurements but "completional" (maybe that word doesn't exist) and as such are incompatible with the progressive/continuous. They're compatible with the perfect.

not OK The new skyscraper had been rising for only ten storeys when the steelworkers went on strike.

not OK I had been eating only three bites when I chipped a tooth.

not OK I had been taking only three sips when a fly landed in my glass.

not OK I had been climbing only three rungs when the ladder gave out.