since you mentioned with one product and HU it is working fine, with two product and one HU you mentioned that it should go to two different storage types, if my understanding is correct then don' t you think physically you should segregate the stock in two different HU. Operation how can you storage same HU in storage type 1 and storage type 2
In my opinion you need to segregate the stock in two different HU and then try to create WT, if at all you want to store two product in same HU then you need to look for mixing indicator, Storage bin type mapping and storage type indicator for both the material should be identical