How is joint contribution calculated over deep tree? How to set max number of elements in joint set, i.e. to doublets or triplets, over a deep tree?

[lynnyi]

I was able to calculate joint contributions over a random forest model trained with max depth = 30 as a binary classifier. My understanding is that, if the path of a particular instance is is 1->2->3->4->5->...->30 in the tree, the joint contributions should be calculated for (1,2), (2,3), (3,4)..., (1,2,3), (2,3,4), (3,4,5)... (1,2,3,4), (2,3,4,5), etc. i.e. the number of joint contributions scales as fibonacci_n where n = depth of tree / depth of path.

For a single instance, I get thousands of joint contributions, but the contribution groups are not what I expect, i.e. the sets of nodes are so disjointed, it doesn't seem to follow one path through the tree, so it can't seem to pertain to only one instance.

So questions are:

1. How is joint contribution calculated for a deep tree?
2. Is there a way to specify a max number of nodes per joint contribution?