Hello,
There is no ideal height. It depends on what material thickness you can get, loss factor of dielectric, maximum thickness allowed for the complete antenna, required frequency bandwidth, production tolerance, etc.
Generally spoken, reducing the height: reduces the useful frequency bandwidth, reduces the gain (because of increase of dielectric loss), does not change the directivity significantly, and increases the edge fed input impedance.
Changing height also changes the resonant frequency somewhat, because of the change in the fringing effect.
If total noise is of importance (reception case for example), you want good radiation efficiency (so gain is very close to directivity).
If you want to design a very narrow band antenna, you also have to consider temperature dependence of dielectric and thermal properties.
---------- Post added at 17:09 ---------- Previous post was at 17:02 ----------
Given your free space wavelength (25mm), dielectric thickness of 134um is very small (0.005lambda free space). Increasing the heigth will probably increase the gain and useful bandwidth.