Various interactions which lead to the observation of sharp EPR spectra of the high half-integer spin impurity Mn²⁺ (S = 5/2) in paramagnetic hosts with integer spins S = 1 and S = 2 have been studied. Studies have been carried out on the basis of data extracted from experimental EPR spectra of Mn²⁺ (S = 5/2, I = 5/2) in single crystals of divalent nickel Ni²⁺ (S = 1) and iron Fe²⁺ (S = 1) perchlorate hexahydrates. The spectra have been taken at X-band (n ~ 9.4 GHz) in a temperature range from 77 to 450 K for Ni(ClO₄)₂· 6H₂O (NiPH - for short) and from 77 to 380 K for Fe (ClO₄)₂· 6H₂O (FePH). It has been shown that the dipolar host-host and host-guest couplings broaden resonance lines of Mn²⁺. Narrowing of the lines in both crystals can be mainly attributed to the host-guest (Ni²⁺-Mn²⁺ or Fe²⁺-Mn²⁺) exchange interactions and to the quenching of the host spins. In the Fe²⁺-Mn²⁺ system a strong narrowing of the Mn²⁺ lines observed at room temperature can be caused by fast Fe²⁺ spin-lattice relaxation. Motions of molecular groups, particularly motions of molecules H₂O, also reduce widths of the lines in EPR spectra of Mn²⁺ ions.