For the door to appear closed the magnets have to be flush, but I also discovered that pretty close is good enough which causes a security problem.
Is just me doing a poorly install of these sensors or are they really so poorly engineered?
Suggestions for other door sensors that works with ST is appreciated 
‘Pretty close’ in practice is actually very close. I’m unsure why this would present a security problem. The sensors would show a break long before the door or window is open sufficiently to cause any risk.
I have a dedicated/monitored Home Security system through FrontPoint/Alarm.com and their door and window sensors allow for some very small ‘un-flushness’ too. But long before the door is open sufficiently to cause any ‘space’ at the edge, the magnetic contact will be broken.
In my case a door can appear closed even when it’s not so if someone fails to shut the door properly (kids) it will be a problem. If the door is really shut and someone tries to break in or open the door is a different story. I guess all this will be solved once I get the smart locks in place.
yes. The new multi sensor that came out this year has a pretty strong magnet and registers closed with a gap of about 1 inch between the sensor and magnet and up to about 0.75 inches sliding. if the two pieces are mounted flush, A door that is ajar (open less than an inch) can be seen as closed.
There are some options if you don’t like this: use a weaker magnet or install the pieces with larger gap between sensor and magnet.
Bigger gap sounds like a plan. I will try that 