You might be on the right track with regards to the additional silicon.

You listed the filler metal be its brand name. That doesn't tell you anything or very little about the composition of the filler metal. You should look at the AWS classification. Then you have something to compare. All you need to do is look at the composition of the filler matal, based on classification, in the filler metal specification. The complete break down of the chemistry ranges are listed, i.e., how much chrome, nickel, silicon, manganese, etc., is in the filler metal for each classification.

In case you are not sure, the classification would look like: ER308, ER308Si, ER308L, each having a slightly different chemical composition, but each would deposit weld having a chemistry that conforms to the AISI alloy 308. The specification for the filler metal would be listed as: AWS A5.9 or ASME SFA5.9. That specification would list all the heat and corrosion resistant filler metals such as: ER308, ER309, ER310, etc.

I suspect the difference you are noting is due to the increase or decrease in the amount of silicon in the filler metal. Increased amounts of silicon provides a "more fluid" weld pool.

Best regards -- Al