You can influence the selection of servers at the same proximity level by adding a weighting value to the autofs map. For example:
/usr/man -ro oak,rose(1),willow(2):/usr/man
The numbers in parentheses indicate a weighting. Servers without a weighting have a value of zero and, therefore, are most likely to be selected. The higher the weighting value, the lower the chance that the server is selected.