DP83869HM: Configuration register for IPG < 12

Hi, our customer is using the DP83869HM for SGMII application, connected to a GbE switch. The switch reduces speed to 1Gbps from 10Gbps. This is reducing the IPG to something less than 12, around 8 or so.

They have previously used DP83867, which has a register 0x53[3:0] to allow smaller interframe gaps with erroring. The DP83869, as far as we are aware, doesn't have this register. This was tested with read register 0x53 (not write) and it contained zero, not the default 5 as expected.

Is there any way to configure the DP83869HM to allow through packets that occur with smaller interframe gaps? Or some way to remove the IPG threshold on the receive?

Thanks and regards,
Tristan