The end of combat messages pretty clearly indicate a +item effect, so after I had thawed the suit down to +5 lbs I killed some beanbats just to get an idea of what number to start zeroing in on.

83 enchanted beans dropped

131 beanbats killed

= .633 beans/bat

divide by the expected .5 and...

1.2671

minus 1.2 to account for the base drop rate and mad looting skills, and...

.0671

So after thawing it looks like it's around a 5% to 10% +items bonus, unless I did some math wrong, which happens.

Unless someone points out a bone-headed mistake I made, the first idea I'll test after rollover is that the item bonus equals the weight bonus.