You have to love the medical professions obsession with archaic, obsolete and plain idiotic terms (i.e. AUC) measurements.

Each unit of French size = 0.33 mm** (may be equal to one freedom size)
so a FR 12 is 4 mm (FR 14=4.6mm) (all that schooling finally paid off!!)
These are quite close and the area (more relevant) of the smaller tube is 75% of the bigger one.

If you are worried about clogging, depending on the viscosity of the Jevity you can always dilute it a bit with water and you will be fine. Also viscosity depends on temperature so you may warm of the stuff a little (probably a good idea anyway).
Re clogging. That happened to me several times but only because I did not blend the vegetables enough (fiber etc) ..... with enough pressure you can clean the tube, but it is s strange sensation + you may make a major mess if it does not work!

Since you are obviously more reasonable than me and are just using it for the intended purpose you should be fine.

Please note:
The pressure drop is more severe for longer tubes. They clog more easily. My PEG was way too long and I trimmed it. (please ask your physician)

Finally:
Size matters, and so does the length of the PEG

Markus

** from the web