Reservation quantity higher than PR qty

Hello Experts

I'm facing the follonwing issue :

Client first did not want PR+Reservation when assigning Material requirement to his WBS. he only wants PR then we changed the item category from L (stock item) to N (Non stock item).

Example :

1/ Activity A asked for 150 cement bags

2/ PR created with qty 150, item category "N". No reservation created on stock

3/ We transform PR in PO, and MIGO for good receipt

4/ We're now ready ask logistics to send us these 150 cement bags  so we made a manual reservation

ISSUE : we're not supposed to make a reservation superior than 150 cement bags, however users are able to ask 200 or 300 cements bags for network.

Thanks for your help

Regards