I deliberately don't make my games full screen because that stretches the stock native PS2 4:3 image to 16:9 and it looks ugly as crap. What I *usually* do is widescreen patch the game's binary to natively support widescreen, but I stopped doing that as - unlike PCSX2, which is mature and capable - the PS2emu on PS4 is much more rudimentary, usually resulting in more graphical glitches and/or performance problems.
~edit~
Play the game for a while, make sure there's no issues or anything, especially performance, and if it all goes well let me know and I can try a WS patch.