Road front derailleurs intended for 50 - 53T large chainrings do seem to shift decently with smaller "big" chainrings as long as you position them suitably close to the ring's teeth.
Shimano's old RSX triple cranks came with 46/36/26 chainrings and used an RX-100 front derailleur intended for a full size 52/42/30 road crank. It shifted quite well.