I've just watched the great youtube clip of Iain showing an elbow and knee combination on a partner, pads and in kihon.
Love the point about recognising flaws in each drill and making up for them by doing additonal drills without those flaws. "Triangulating" the result you are after from multiple directions.
BUT...I couldn't help wondering if the deficiencies in the padwork drill couldn't in some ways be mitigated by using the Thai pad holder set-up rather than just focus mitts?
Having a partner with two Thai pads and a belly pad would mean you wouldn't need to use two pads per elbow (Thai pads have more mass than focus mitts so don't necessarily need double bracing in the same way) while the belly pad would provide a place to impact the knee (not the groin but near enough) without needing to get both hands down to it (and just using one pad per elbow would mean you had a pad free to move down to augment the belly pad quickly anyway).
Thai pads aren't generally as quick to move and position as focus mitts so they aren't without their flaws but I felt in this sort of drill they'd be a real bonus.