PO Document with Security Level Set to Hierarchy is not accessable to people in Hierarchy

Hi All

For Standard PO document Security Level is set to hierarchy.

Level 1 has approval limit 0.1, He is Raising the PO with 
Level 2 Approval limit is up to 10,000 AED, He Can approve any PO
Level 3 Approval Limit is up to 99,000,000 So that he can approve any PO.

If PO value is 9000 AED,  PO gets approved by Level 2 Person successfully,
Problem is Person at Level 3 cannot search the PO or access it regardless of the fact that he is in Hierarchy.

Any help or solution will be highly appreciated.

Regards

ASIF