Better driver, worse system performance?

I'm desperate looking for help.

My project is a balanced 1W(average) OFDM PA at 600MHz, droven by a half watt class A driver. The original design is very close to system requirements, except marginal fail EVM, which I think caused by the driver. So I found a drop in replacement driver and evaluated it. With new match circuits, the new driver alone performancs very good--2dB higher P1dB and 1~2dB better EVM.

What confused me is that system EVM drop by 2~6dB! 8O

I don't think the driver change would impact the final stage because there is a 50ohm splitter between them.

Any idea? Please.

put a pad between driver and final amp.
This will cause EVM to normal and lead P1dB to original.
Note that P1dB is not main trade factor then EVM.

Thanks , kspalla.

I wonder how a pad would help EVM that way? I understand it would lead the driver P1dB to original, but the driver's EVM would be worse because to maintain the same power to drive final stage you need more power into the pad.

Can you explain more?

Above discussion, assumed that driver is free with EVM issue. it it has the issue then final PA will just carry the same EVM.

First ensure that driver is satisfying EVM.
i mean to say by getting higher p1dB by the driver, and over driving the final PA causing EVM to fail.