It is true, that measuring can be done with one sensor, when you calibrate the needed measure range.
Method used when you calculated : Right sensor value should be near >> (left sensor) * (line F1) / (line F2)
Before you can calculate any force vector, you must realize and calculate
all the force vectors simultaneously and together.
You have to know, where the force generated by you is transferred to the plate surface,
and how it is divided to the external support points and the sensors.
I take an example:
If plate is supported like window screen, your added force is divided to all directions.
because of an infinite number of the support points are located in the edges of the screen.
Minimum number of the supports needed to put screen on table is 3.
2 sensors and 1 additional point.
Can you show me , how is the screen is (fixed ) supported, it can´t float in the space.
Or it is window like this....
KAK