Request clarification on few points in BOE functionality

Please can we have the confirmation/clarification on the below and if the below statement is correct:

1) Can the tax category be derived automatically only for BOE/receipt and not for PO creation ?

2) Assessable value defaulted in PO will default in BOE. If different assessable value has to be entered during BOE creation the 'assessable price list' field has to be made null/blank first so that different assessable value can be entered during BOE. Tax will be calculated as per updated assessable value.

3) If 'assessable price list' defaulted from PO is not removed then in BOE the assessable value even though changed in header will not be updated/passed to lines (when apply button is clicked) and tax will not be calculated with the updated assessable value as 'assessable price list' field is not made null/removed.