Sorry, Wish I would have read this thread when it started. 20+ years as a certified NYS Pest Control operator and plenty of experience with honeybees, yellow-Jackets and Balled-Face/European hornets.
We used to mix Cyanide powder (Cynogas) with Sevin powder so we had a knockdown and a residual and then pumped the dust it into the nest ( BTW, I was never aware that yellow-jackets had 2 entry/exit holes - Complete news to me).
Anyways, if it isn't too late, send you bee suit back and get a couple of tyvek suits, one that fits you and one the next size larger and wear them together on your test runs:
Tyvek Suits from Aircraft Spruce
and then call Campmor and buy one of these:
Campmor: Mosquito Head Net
and you will be all set.
Another trick - We always took care of these vermin either at dawn or at dusk on nice days, or usually anytime on cold wet raining days.
However, I got in the practice of always keeping a lit cigar in my mouth and constantly keeping a Little cloud of cigar smoke around me.
Believe me the cigar really worked great when I was on a 40' extension ladder (or cherry picker) doing a church steeple or 3rd story roof-line.
The problem with spraying liquid insecticide at the entrance to the nest is that you piss them off and they will find another way out and the queen usually makes off to build a nest somewhere else - I even once saw some BF Hornets carrying their pupa with them flying out of the nest.
Anyways, sometimes it is a very good idea to make some fast passes with your tractor and your new suit on, with your implement hanging low to disturb vegetation (but not turned on yet) to try to stir up trouble. A few fast passes on the are you are palling to work ( as well as any adjoining areas) and you will know if you have an underground nest.
I always also scan trees looking for the grey oblong nest - a surefire telltale sign of vicious hornets.
Also keep in mind that honeybees die after a sting. Yellow jackets and hornets can sting repeatedly.