I don’t think you will ever get good presence (or occupance) detection based on motion detection alone, integrating more sources of information will probably give better results.
I have started developing an app based on bayesian statistics (https://en.wikipedia.org/wiki/Bayes’_theorem). I am using a node js library which you can ‘train’ with ‘good’ and ‘bad’ datasets (‘good’ and ‘bad’ can be mapped to ‘someone is present’ and ‘no-one is present’). If you then present the library with an actual dataset, it will give you the probability of someone being present or not.
The initial concept is based on a data set containing selected ‘better logic’ variables and the on/off state of devices with onoff capability. The dataset can be expanded to include any binary state. The selection of the variables is important, you do not want any use any devices that are also used for your alarm for instance, or in general variables that can be influenced/manipulated by others (ie. non-family members ).
Useful BL variables can be ‘high’ or ‘low’ power usage, or things like if your TV or audio system is on (preferably based on the power usage as well, so you know they are being used) which are strong indications someone is at home. I have Homey switch on the mechanical ventilation in the bathroom, which only happens when someone is showering or taking a bath, so that’s a good one as well, and you could perhaps use things like the temperature in the living room and get creative with things like that. And of course sockets being switched on or off, and the presence states as indicated by various apps (Homey presence, Unifi, Tado, smart presence, what have you).
I expect that combining all those variables and training the library on the two states (‘someone present’/‘no-one present’) in various conditions will give good results.
I have a working concept app, it has a button in the mobile interface so you can train the app with different scenario’s. I stopped developing it a while ago as the app requires an elaborate settings page which is quite different on Homey V2 compared to V1. I plan to rewrite one other app before I switch to V2 myself, after that I will probably pick it up. The groups app @Jamie made looks like it may be a good starting point for the settings