If you look at the total equation for the Debye length, which basically determines your sheath thickness, as you can see here: https://en.wikipedia.org/wiki/Debye_length

you will see that a larger value of T_i will increase the Debye length and that is the reason why the sheath thickness increases for a fixed potential.

Thompson and Boyd researched the potential of Bohm for electronegative plasmas as early as the 1950s. Studies have shown in latest years that the Bohm equation encounters numerous alternatives for an electronegative plasma sheath when the temperature ratio of electrons to negative ions is greater than a critical value of 5+ √24 and the minimum of these should be the physical answer. Shindo et al. researched the behaviour of the floating potential and sheath thickness corresponding to the Bohm potential multivalue, and by incorporating the Sagdeev potential, also,Yamada and a coworker studied the structural instabilities of the Bohm system. In addition, Deutsch et al theoretically explored the impact of both negative ions and secondary electrons on the collision-free sheath. A one-dimensional fluid model of electrons (positive ions and negative ions) combined with Poisson's equation was created to describe Amin et al.'s self-consistent conduct of the unstable sheath framework, and a comparison of a Monte Carlo simulation of a parallel-plane radiofrequency (RF) powered oxygen plasma with the outcomes predicted by a macroscopic analytical model was presented by Lichtenberg et al. You must also consider that Palop et al. have recently used the Maxwellian speed distribution features of both electrons and adverse ions to explore the sheath structure of aircraft samples in an electronegative plasma, and the double sheath structure has been studied in electronegative plasmas with photon emission. I think you should read these literatures to have a complete understanding of the actual picture.

Johannes Gruenwald Vijay Chatterjee Thank you for your valuable suggestions.