The 737CL apu seems to be the more troubling of all the twin engine airplanes, I definitely see the failed starts on the ground with this type; it eventually gets cranking after a few tries but can understand why a pilot might start on descent, into a remote or poorly served port. But all other twins seem to be reliable enough, in my experience.
The mx requirement on A330 to select Master switch ON and wait approx 3mins before start, is to prime the APU fuel system, the fuel pump specifically if I recall correctly, to prevent cavitation. But that is a mx req.
if an operator/airplane is ETOPS certified, the apu is condition monitored and inflight starts may be required from time to time in addition to other apu reliability tests and checks as part of the normal mx program... these inflight test starts will occur specifically whilst the apu is cold soaked to ensure a successful start, if not, it gets looked at. This is what SHOULD be happening. but I recognise not everyone does the same thing and there are differences between some mx programs and mx staff competency.
Bottom line, I would recommend sticking to official guidance. If your apu doesn’t work the way it should whilst cold soaked, on the ground, then this is exactly where you want to find out about it! Log it, get it fixed! Don’t be part of the problem.