Most of my mature buck kills have been within 20 yards.
This is in large part because most of your hunting involved "set-ups" where a deer was mostly likely to be encountered at @ 20 yds, and beyond 40, unable to be seen?
I've also taken most of my mature bucks in heavy cover.
But believe this is large part because of how I hunt,
as do know many people killing more than I just by sniping them at extreme long range,
and, yes, many are out in large fields.
To some degree, deer, including mature bucks, can become "conditioned" to the point "generalized abnormal" behavior
CAN become a particular deer's "normal" behavior.
I've seen deer become "conditioned" (mainly due to a lack of human disturbance) to bed & feed during daylight in very open, mature hardwoods (where they're easily seen, even when bedded, over 100 yds away by a hunter). But this type behavior usually only occurs with the lack of hunters, the presence of which contribute to deer "generally" having different primary bedding & feeding areas.
Then there's the issue of routine human behaviors "conditioning" deer to ignore those humans, such as farmer checking on his fields or livestock regularly, or vehicle traffic on a busy road.
Deer often become "conditioned" to ignore certain human activities, even certain individual humans. Deer that grow up around lots of water will often just swim across a large body of water rather than walk around it. Same for large fields, when they're not accustomed to being shot at for doing so.