OTM Order Priority

We are using OTM 6.4.3 and we are trying to implement order priority in the planning parameters

but seems it is not working properly

we have 3 orders with

7401168_1 => priority 60

7401052_1 => priority 70

7401169_1 => priority 80

and expected result would be

Shipment 1 => All of order 7101168_1 and half of order 7401052_1

Shipment 2 => Half of order 7401052_1  and half of order 7401169_1

Shipment 3 => Half of order 7401169_1

Thats is to consider planning to be based on priority

But planning happens as follows:

Shipment 1 => All of order 7401052_1 and half of order 7101168_1

Shipment 2 => Half of order 7101168_1  and half of order 7401169_1

Shipment 3 => Half of order 7401169_1

Any idea, what can be done?

Thanks in advance