**Favor 12" OC joists over extra rows of blocking**, keeping the blocking already specified. For otherwise identical framing, closer joist spacing is the more dependable way to improve firmness.

Blocking restrains joist twisting and can help neighboring joists share a footstep load. But it does **not shorten the unsupported span or increase each joist’s bending stiffness**. Its benefit depends on the connections and the whole deck assembly; extra blocking alone will not reliably eliminate bounce. [Research on between-joist bracing](https://napier-repository.worktribe.com/output/1147003/influence-of-stiffness-of-between-joists-bracing-on-vibrational-serviceability-of-wood-floors)

Changing from 16" to 12" OC gives you roughly one-third more joists and shorter spans for the decking boards. Under an evenly distributed load, each identical joist carries 25% less load, so its calculated bending deflection is about 25% lower. That does **not** translate directly into 25% less bounce under a footstep.

For the solid feel you want, also consider:

- **Deeper joists.** Joist bending stiffness increases approximately with the cube of their actual depth.
- **Shorter unsupported spans**, using another properly supported beam if practical.
- **Stiff beams and appropriate post spacing.** Flexible beams can make the whole deck bounce despite closely spaced joists.

Assuming your beam is about 12' from the house, you have roughly a **12' supported span plus a 2' cantilever**. Both need checking against the selected joist size, species, grade, and local requirements; a 2' overhang is not automatically acceptable. The [AWC deck guide](https://web-media.awc.org/wp-content/uploads/2022/02/17210514/AWC-DCA62015-DeckGuide-1804.pdf) checks the span and overhang separately.

My choice would be **12" OC with the planned blocking, then size the joists and beams for stiffness rather than using their maximum allowable spans**. Without the joist size and beam/post layout, neither spacing nor extra blocking can guarantee a spring-free deck.