Target AFR above 14.7 on stock Subaru ECU

Hello, my task today is getting my own daily driver (a 2005 Subaru Legacy GT) to run a commanded AFR. I am using "open source" software to achieve my tune in the sense of ECUflash for reading and writing the ROM and romraider to achieve the calibration on the file. I am running the factory ECU.

One limitation I seem to be having is the stock ecu software (or possibly a romraider limit) seems to have a max commanded AFR in the open loop tables of 14.7 although I would like to target an AFR in the idle and cruise regions of the map to be 15.2 range to experiment with better fuel economy. I though about how to work around this with possibly a compensation table and making it something like when engine coolant temp above 140 then fuel target * 105% to achieve a 5% fuel reduction but I dont think I did this correctly as I seem to still get an AFR of 14.7 on my wideband. Or could I be possibly trying to achieve something that the ECU just refuses to do?

Any help is appreciated!

In OE applications there is no reason to target a leaner AFR than stoichiometric so it's likely that this is a hard coded limit. In closed loop in particular the narrow band oxygen sensor can only target stoich too. You could probably work around this if you're running in open loop by offsetting the MAF scaling in the area you want to tune leaner.

you can achieve that by re-scaling the Narrow band O2 sensor table.