Nondimensionalizing a mixed predator-prey system

Question

I want to Nondimensionalize the following system $$V'=rV(1-V/K)-aVP,$$ $$P'=-sP+abVP.$$ Which is a predator-prey system where we consider a logistic growth for the prey instead of a malthusian one. I know how to proceed when both are logistic or both are like the Lotka-Volterra ones, but in the mixed case none of the variable changes seems to work. Any help will be very appreciated. My advances so far: Take $x=V/V^*$, $y=P/P^*$ and $\tau=\alpha t$ for some constants $V^*, P^*,\alpha$ to determinate. Then we have $$\frac{dx}{d\tau}=\frac{r}{\alpha}x-\frac{r}{\alpha K}V^*x^2-aP^*xy,$$ $$\frac{dy}{d\tau}=\frac{-s}{\alpha}y+\frac{abV^*}{\alpha}xy.$$ Taking $\alpha=r$, $\beta=s/r$, $P^*=r/a$ and $V^*=r/(ab)$ i end up with $$x'=x-\frac{r}{abK}x^2-xy,$$ $$y'=-\beta y+xy.$$ I dont know how to conclude it