Because you divide t30 by 1000, your t30 will end up slightly over 0.1 apart from each other. To reach as high as the [0 10] upper bound of the fplot, you would need to be plotting about 95-ish points. Do you have that many?
It is not generally a problem to hold on and plot over an fplot, provided that the range of values is large enough to cover a notable fraction of the area.
syms x
f = x^2 .* cos(x)
fplot(f, [0 10])
hold on
plot(0:5, [.1 .5 -.1 3 4 -2])
