how to avaide overwrinting results in drools planner

[Ricardo]

I have 2 boxes, lets say each size of 5x5 and I have 3 items two size 4x4 and one item size is 3x3. planner initially planner assigning as follows...

I - When I use 3 items 2 boxes....(this produce wrong planning)

item1 (4x4) --> box1 (5x5)
item2 (4x4) --> box2 (5x5)
item3 (4x4) --> box1 (5x5)

II - When I use 2 item, result as follows...(this is correct planning)
item1 (4x4) --> box1 (5x5)
item2 (4x4) --> box2 (5x5)


III - When I increase one more box....(this is correct too)
item1 (4x4) --> box1
item2 (4x4) --> box2
item3 (4x4) --> box3


you can see the test I - it is over writing the first assignment and assign the new item there in the box 1, I unable to figure it out how to solve this problem, I suspect this can be done in the score calculation rules, the problem is I do not know how to implement to avoid the overwriting assignments.

thanks,