I'm sorry you didn't understand my posts correcting you duct dr. I am also sorry that you just want to argue to the point of again posting wrong information. If all you want to do is to pass on innacurate information that "you heard", then I will continue to correct you.
Here is your current correction;
There is no such thing as a 3 ton coil so it is innacurate to state that "a 3 ton coil is a 3 ton coil and they are all the same size." That is just wrong.
The higher the efficiency, the larger the outdoor coil must be. The larger the outdoor coil must be, the larger the indoor coil must be to accomodate the amount of additional refrigerant in the system.
However; by installing a TXV we can reduce the physical capacity of an indoor coil because we have a variable metering device that will contiue to regulate the system superheat despite the smaller coil capacity.
This is exactly what we strive to do to increase dehumidification in humid areas. Also, it is a good practice to use TXV metering for a system that is going to operate in cooling at lower outdoor temperatures and/or low loads.
A TXV also allows the efficiency rating to increase without making the coil larger to match the higher efficiency outdoor units. You can add additional SEER points by either adding a TXV or by increasing the size of the coil. This is where the cost factor of TXVs actually saving money on the cost of building coils comes in to play.