Abstract In this paper, we discuss the results from the two-dimensional computational investigation of the effect of a helium plasma jet interaction with dielectric plates at a floating potential positioned at different angles (α = 0°, 10°, 30°, 45°, 60°, and 90°) relative to the vertical axis. We show that greater surfaces can be treated when the plasma jet is applied non-perpendicularly to the plate. The case of α = 45° is discussed in detail. Here, the dielectric properties (conductivity σ and relative dielectric permittivity ε/ε ₀) of the plate were varied. By introducing notations D (deviation of the ionization wave from the tube axis) and S (plasma treated area) we showed how these values are related to the dielectric properties of the plate. We demonstrated that D and S weakly depend on the conductivity σ when it is below the level of (3–5) × 10⁻⁴ Ω⁻¹ cm⁻¹. In this case, the deviation D and S are mostly determined by the relative dielectric permittivity ε/ε ₀ of the plate. By lowering the dielectric permittivity (at a constant σ) we increase the treatment area S. For conductivities of 10⁻³ Ω⁻¹ cm⁻¹ or greater, D and S do not depend on the permittivity of the plate. In this case the treatment properties are totally determined by σ. The indicated value of conductivity is close to the conductivity of tap or sea water. It is also close to the conductivity of the inner parts of cells, for example, the cytoplasm of human skin cells. The results will be of interest for researchers working in the area of plasma medicine.