It is indeed a larger FPGA, it's a Cyclone 4 device EP4C6E which has 30k of onboard ram. That's compared to 13k ram on the Cyclone 2 EP2C5.
The original build MFX used the internal ram for the 80 column board memory, plus buffers for the sprite rendering on the VDP. The external chip was used for the 16k VDP memory. The other 16k external memory was connected, but not actually used for anything.
Bill then re-wrote all the video handling for the January release, that introduces all sorts of goodies including the USER VGA 2 mode 80 x 48 text screen and the 320x240 bitmap modes that make full use of the 32k vram. Since 8k of internal ram is also being used, the current MFX builds are using up to 40k for video ram
Building the January release code for the cyclone 4 board revealed a REALLY nasty surprise. The VGA display was awful**. It looked just like the original VDP output on the composite. There were VERY visible hum bars, no need for retro mode on THIS board!
As a potential FPGA alternate board for the MFX it was a non-starter.
However, not wanting to give up on it enturely ...
I tried removing the external ram and taking a step back to the original 2 mode video design which used just 24k I have got that running using the internal memory and the display is just as crisp as the original. And while it sort of works with the new rom, it's not really useable for anything other than VDP mode. Using the 80 column display requires the original 167 rom.
As a proof of concept, it worked. As a 2nd source board for MFX it's a step backwards
** The guy that designed it uses it in pinball machines, so it's never been used to output VGA until now. I tried a few simple board mods like adding more power regulation but that didn't help.