Inperpolated position mode is designed so that the master sends an array of positions and the drive does a movement that follows the positions by interpolating between them. There is an interpolation time period set in objects 0x60C2:0x01 and 0x60C2:0x02.
The way the Trio master uses interpolated position mode is to set the interpolation time the same as the servo period and send it one position. The drive then interpolates between the previous position and the new one. The effect is that it is the same as the way CSP works.
In CSP mode the master sends a new position every cycle and the drive moves immediately to the new positon. Some drives have an internal period that is shorter than the EtherCAT period. In those drives they do an inerpolation between the positions sent by the master. For example the drive has internal position loop at 200 usecs and the EtherCAT cycle is 1 msec. The drive calculates 4 points in between the CSP points and interpolates between them.
Conclusion is that there is not much difference between the modes in the way the Trio Master uses them.