Clock Skew reported from transceiver PHY to user logic

Hello Experts, I need your help.

I have a simple UDP offload design (10G using two ethernet ports). I have two flavours of Stratix V GX FPGAs, an A7 and an AB (5SGXEABK2H40C2). When I build the design on the A7 FPGA, it builds fine and meets timing comfortably. However when I build it on the AB it has problems, namely within the Ethernet controller - specifically between the TX MAC portion and the PHY. The TimeQuest timing reports a setup violation on the TX clock/path. The negative slack is very minute around -0.06. The recommendation points towards clock skew and asks me to use global clock resources (currently using periphery resources via ALTCLKCTRL) for the source and destination clock. I tried using Global and Regional and the results was much worse. The problem I have is that the MAC portion is hidden third party IP so cannot modify. So I am wondering what to do?

I have tried the following:

- tried changing to global/regional clock

- tried all types of optimisations within the fitter settings and including aggressive performace

- tried locking logic closer to the PHY

Nothing has improved it by much. Any ideas would help.

HaHaHa.