Amazfit Watch faces

Hi there all, I am currently making a watch face and running into a peculiar problem. I am generating the text PNG's in photoshop, a simple letter, rasterise and trim then save to PNG, however for smaller letters and numbers (below 30px) when shown on the watch, they show up somewhat pixelated, and for the life of me I can't figure out what the reason is, I have tried different anti-aliasing in photoshop but to no avail, but I know it's possible to use the font in smaller sizes as there are other watch faces using it (Rajdhani Bold).

Any advice would be appreciated!