I'm curious if you also saw a power increase. The 43v firmware should allow a few more amps vs the 48v firmwareHi.
I will describe a small experience I had with using two firmware versions in my LEC930 which has a 48V DIY battery installed (13S3P LG 21700 M58T).
1. For the first trip to the mountains with this bike, I had the 48V firmware installed: CRX30PC4812E102006.3 (I didn't notice that it was an eRoad), it rode very well on flat ground, but on uphill sections it was hopeless! the feeling as if the power was being cut all the time, no matter in what mode, and the power seemed to be wavering (sine wave), it did not resemble the support I had ever used before (Shimano, Brose). Overall, I was very disappointed with the engine's performance.
2. Before the second trip to the mountains, I searched the forum, then I noticed that I had the eRoad version installed and additionally I came across a post by user #DADO which concerned the M510 engine and the possibility of uploading software for a lower battery voltage to make greater use of the battery's potential (for 48V firmware - Bafang shows 20% of the remaining battery capacity while its voltage is still ~46V (3.54V per cell, where it could easily be discharged to 3.0V per cell).
Following this path, I uploaded the firmware for 43V: CRX30PC4313E102001.3 (eMTB) and after many tests at home and checking the parameters with BMS software, I found that it looked safe for the engine...
So to the mountains! the route I took was more demanding than the first one and the engine operation was completely different - amazing! it was what I expected from the support and I didn't need any modes other than ECO and TOUR (long years on an analog bike certainly helped) and the climbs were really solid. I will add that the engine warmed up in the same way as before - only checked organoleptically.
So if you have the impression that the engine cuts out power when going uphill, you most likely have eRoad software installed.
If you also want to use the potential of your DIY battery to a greater extent and are aware of the risk of damage, upload the firmware for a lower voltage battery at your own risk.