Its a mystery to me how this actually works at all.
I must be reading this wrong, as I feel the cap is in the wrong place and reversed. (the neg terminal is at a more positive potential than the pos terminal).
As to my way of thinking, the drain is at a lower potential than the source in your diagram. Usually, a conducting diode closes the circuit on the inductor when the fet turns off. In this case (to my thinking anyway), then the body diodes would perform this function. This may explain why adding conducting diodes made no obvious difference.
In it's current config, it may struggle... but work. The back emf generated by the conductor may current spike the fets body diode though, so this just doesn't work for me.
By changing the pot reference point, you would make the gate more negative with respect to the source, and this should turn it off I guess, but it just seems all wrong... the gs voltage may go excessive when the fet is open..... ie the source will go to gen+ almost, while the gate is tied to the drain by the pot.
Note, I have not built a buck, but if I did, it would not be in this guise, if it works well like this then .... but the fets seem vulnerable.... and the cap is still wrong to me.
I may be completely wrong with this, but it just do't look right.
.........oztules