Perhaps Ernie is confident that after all of last season, the squad knows how to play 4 - 3 - 3 and 4 - 4 - 2 (diamond, or no diamond), so if 3 - 4 - 3 (or 3 - 5 -2) ends up not being plan A, he probably feels we can switch to plan A at any point, so why not maximise the amount of time the new formation gets to bring it up to speed?
Perhaps Ernie is confident that after all of last season, the squad knows how to play 4 - 3 - 3 and 4 - 4 2 (diamond, or no diamond), so if 3 - 4 - 3 (or 3 - 5 -2) ends up not being plan A, he probably feels we can switch to plan A at any point, so why not maximise the amount of time the new formation gets to bring it up to speed?