Without seeing your whole code it is a little difficult to be sure what the problem is, but it is most likely that the range of frequencies that your are evaluating the nyquist frequencies is starting at too large a frequency value.
Note that the Nyquist plot that you show is not generated by your call
[re,im] = nyquist(zp+zt, increase_amount_of_Values)
as calling nyquist with left hand arguments will not produce a plot.
So you are probably looking at an overall plot with autoscaled frequency ranges from an earlier call to nyquist. This may be leading you to believe that the range of frequencies you are using are appropriate.
I would suggest first calling nyquist without left hand arguments but using what you think are a good range of frequency points. You will then see from your plot whether the range is appropriate.
Once you determine an appropriate range of frequencies you can call nyquist with left hand arguments to get the values you need