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If that is the rim joist at the end of the logd, get at leas 3- 4" of insulation there. Cut some foamboard to fit as close as possible then use cans of spray foam to glue them in place. That can be a huge heat loss area.

I would just put fiberglass batts against the plates, 6" or more if the space is cold. You will need to make some custom length wires to hold he insulation in place between those logs?

How thick is the floor build up, the planks plus the finish flooring?

do you think it will be more efficient if it runs more than 120 hours biweekly ? I just disable outside reset temp and set the water temp to 135f. The return is coming @ 126f. I will take a lot at the consumption tomorrow. For context, the outdoor reset temp was always @ 150f.

yes - that boiler can modulate so during especially cold weather it should run near nonstop. 150F was too high, 135F is a good temp to try. Lower temps at higher outdoor temps is the key.

It sounds like the choice of a mod/con boiler with baseboard heating is a questionable choice for your location and building type. The "lowest hanging fruit" for you to "grab for" at this point is building envelope improvement i.e. air sealing first, then improve insulation. Then, you can focus on improving the operation of your boiler by 1. reading the manual 2. having a combustion analysis done, 3.installing the outdoor sensor and dialing the boiler in to all of the appropriate settings. This is the best you can do right now with what you have. You could install some more baseboard in the future. In the end, your fuel bill will inform you HOW WELL you did!