Bypass full open?

I have a bypass installed with ball value. It was closed during the summer, but I opened it for the winter after noticing the temp of the boiler dropping a lot when circulating hot water for the baseboards. It seems to reduce the temp drop in the boiler when the heat is on multiple zones. I also reduced the temp of the L6006 to 120 (had it set to 140 in the summer) that I have for sensing fire outage after watching the boiler temp swing with the value closed. Should I leave it full open during winter and summer?

Thanks,

Dave

The idea is to force some of the returning water back into the radiators to prevent your type of problem. Adjust the valves so that a portion of water is forced back to the radiators.