Hello, before v13 I use OCA's addon Stock MTS+MTO Rule (https://apps.odoo.com/apps/modules/12.0/stock_mts_mto_rule)

in v13, this feature should have been integrated, but seems like needed additional configuration.  

Behavior in v13,

Product_A routes are Buy and MTO.  Vendor and price are set.  No reordering rule.  On-hand qty is 10, no reserved qty in stock.  

If SO contains Product_A qty of 10, PO is not generated.  This is good since even MTO is set, v13 still checks inventory.  

If SO contains Product_A qty of 15, PO is generated but with qty of 15 not 5. 

The correct quantity is 15-10=5 in PO.  

The wrong qty is 15 which doesn't validate on-hand.

Further more, if there's a reordering rule is set to min=0, max=0.  The PO qty will be 15+5 and turned to 20.

Could anyone confirm the above example is by design of v13? 

Could I configure v13 to behave as v12 with stock mts+mto rule?

(I need PO source document to be SO number, not re-ordering rule number.  Therefore, I cannot rely on using only Buy route + Reordering Rule on every product.)