This is the desirable output from blast furnace, lower HM [Si] with good HM temp. this is an indication of good thermal condition, well placed thermal and chemical reserve zone in blast furnace.
High [Si] and Low temp could be due to 1) poor HM and Slag separation ( conditions normally seen in furnace startups: Si diffuse to HM, HM and slag interface reaction). 2) Higher Slag rate, 3) Increased in Ash % in Fuel- coke /coal 4) Delay in Tap Openings (Higher residence time of HM in Hearth)