The data rate of dv is constant. I think ep mode just squeezes everything into tighter tracks so less tape is used.
This is likely to increase the drop out rate and make the recording unreliable.
" DV on SP has a helical scan track width of 10 micrometres, while EP uses a track width of only 6.7 micrometres. Since the tolerances are much tighter, the recorded tape may not play back properly or at all on other devices. "