I think you are getting closer, but you still seem to be confusing "fully turned on" with operating the mosfet in its saturated region. When the mosfet/gate is not fully turned on, it is not acting as a switch. Increasing or decreasing the gate voltage will affect the resistance between the drain and source (Rds). With a fixed voltage on the drain, you will see the current (Id) change as a function of the gate voltage relative to source (Vgs).
As a switch, when the mosfet is fully turned on, Vds should be quite small (Id*Rds).* If you see a large and increasing Vds with minimal increase in Id (i.e., the mosfet is in its saturated region), the mosfet effectively cannot handle more current and heat is produced.
John
*This fact explains why Vg must exceed Vd if an N-channel mosfet is used in the high configuration, i.e, load is attached to source.
As a switch, when the mosfet is fully turned on, Vds should be quite small (Id*Rds).* If you see a large and increasing Vds with minimal increase in Id (i.e., the mosfet is in its saturated region), the mosfet effectively cannot handle more current and heat is produced.
John
*This fact explains why Vg must exceed Vd if an N-channel mosfet is used in the high configuration, i.e, load is attached to source.