prepositions - Difference between "As For" and "As To"

1a. an explanation as for what happened
1b. an explanation as to what happened
2a. As for funding, the committee might have a meeting to address that.
2b. As to funding, the committee might have a meeting to address that.

Is there a subtle difference between "as for" and "as to"? Dictionaries pretty much say that both mean "concerning" or "regarding".