You can only ever have one IFR aircraft ( that hasnt reported visual) in the BK CTR at one time. My understanding is the APPCH permission from SY CEN is for sequencing into BK even though you are OCTA from SY airspace for the majority apart from the aformentioned segment of the IAF-IF leg, which without a clearance to enter ( different to approach permission), you must avoid.
Just out of interest, is this 'procedure' published anywhere? ERSA, DAP's/Jepps?