This study measures the fluctuation parameter F in the Macquart relation, which describes the correlation between the dispersion measure (DM) of fast radio bursts (FRBs) and the redshift z of their host galaxies. Using 78 FRBs, including 21 with localized host galaxies, the researchers analyze the distribution of DMs from the cosmic web and the impact of galactic feedback on the intergalactic medium. They find that the fluctuation parameter F is degenerate with the Hubble constant H₀, and use a uniform prior on H₀ to measure log₁₀F > -0.86 at the 3σ confidence level. They also determine a new constraint on H₀ as 85.3 ± 9.4 km s⁻¹ Mpc⁻¹. A synthetic sample of 100 localized FRBs improves the constraint on F by a factor of ~2. Comparing their results with cosmological simulations (IllustrisTNG), they find agreement between redshifts 0.4 < z < 2.0, but simulations underpredict F at z < 0.4, which they attribute to the rapidly changing extragalactic DM excess distribution at low redshift. The study highlights the importance of understanding feedback processes in galaxy formation and their impact on the intergalactic medium. The results suggest that the Macquart variance is a measurable observable, providing insights into cosmic feedback and cosmological parameters. The study also emphasizes the need for future surveys to improve constraints on F and better understand the distribution of baryons in the universe.This study measures the fluctuation parameter F in the Macquart relation, which describes the correlation between the dispersion measure (DM) of fast radio bursts (FRBs) and the redshift z of their host galaxies. Using 78 FRBs, including 21 with localized host galaxies, the researchers analyze the distribution of DMs from the cosmic web and the impact of galactic feedback on the intergalactic medium. They find that the fluctuation parameter F is degenerate with the Hubble constant H₀, and use a uniform prior on H₀ to measure log₁₀F > -0.86 at the 3σ confidence level. They also determine a new constraint on H₀ as 85.3 ± 9.4 km s⁻¹ Mpc⁻¹. A synthetic sample of 100 localized FRBs improves the constraint on F by a factor of ~2. Comparing their results with cosmological simulations (IllustrisTNG), they find agreement between redshifts 0.4 < z < 2.0, but simulations underpredict F at z < 0.4, which they attribute to the rapidly changing extragalactic DM excess distribution at low redshift. The study highlights the importance of understanding feedback processes in galaxy formation and their impact on the intergalactic medium. The results suggest that the Macquart variance is a measurable observable, providing insights into cosmic feedback and cosmological parameters. The study also emphasizes the need for future surveys to improve constraints on F and better understand the distribution of baryons in the universe.