compound calculator is just an alpha test which is incomplete yet, it doesn't support superior yet thats why +5 is not implemented
also compound calculator is still using average ranks + 4 to find max rank
so here the calculator thinks
12 + 18 = 30 / 2 = 15 + 4 = 19 as max rank
IGN = taisan, Guild =*none*, Server =Leo1
timezone = GMT +5:00 (Maldives)
Spoiler: