i used to use metaborate as a B bath but concluded after testing that, unless i specifically wanted the fine grain look of metol 85g/L sod metaborate 12g/L, i prefered the look of sod carbonate 20g/L - total development in bath B. mid tones, to my eye, separate well ( by printing at grade 3 - 3.5 ) without the highlight being too problematic ( highlight gradiation is also maintained ).

what splitting has done is lowered the sulfite content, improving perceived sharpness. i never understood the benefit of having the extra 50g thrown in bath B. perhaps someone will chime in. if you like the look of sod sulfite 100g/L ( which suggests to me you want smooth tones at somewhat the expense of sharpness then pursuing max absorption at bath A and local development in bath B may be counter to that look?