Most of the winter rain just goes straight through the drains, its been doing that since the first week of Oct here so if we got it at the right times I think 400mm would be perfect, we had under 45mm in May/June 18 and the biblically crap spring did more damage than the dry.400 would work if temps peaked at 23-24max June July with one proviso... 200 mm needs to fall april, may and june.
400 is a bloody disaster if 50 or less falls may june.
Sodden winter followed by dry or very dry early summer is the single worst scenario.
Dry winter followed by cool and wet ( by our standards ) early summer is "grain shed isn't big enough"
300-350 mm being enough here is a laughable idea ( otherwise you would cry).
91/92 growing season iirc, maybe 92/93 was 12.5 rain-guage inches for the growing year, and it wasn't funny.
Longer daylight means more evaporation, warmer soil and air temperatures also make a noticable difference .Got some more slurry spread yesterday, quite remarkable how the field had dried over the past few days despite some showers, but that's spring for you, in the autumn the weather can be dry for several days without the same effect. I've often thought that soil conditions are not just a matter of physical properties, the season has some sort of effect as well, yesterday pretty much clinched it for me.