Are there other pawpaws nearby? The trees are mostly self-incompatible and require cross pollination to produce fruit.

It sounds like you need another variety for pollination. Usually flies and beetles will do the job, but it is better if you use a small fine paint brush for hand pollination from another variety to ensure fruiting. I don't think taking out suckers have anything to do with fruit set.

Tony

There is a nearby pawpaw that for the first time produced a dozen large fruit last year.
I've attracted insects with fish heads, chicken necks and fat.
(see link)
There were so may bugs this spring that even spiders were roaming amongst the flowers.
At what stage of fruit development can I consider abortion a failure of pollination vs. failure to fruit for another reason. i.e. are these green 'rice grains' a sign that pollination has occurred?

Here is a link that might be useful: attracting insects

Those fruitlets appear to have received the benefits of pollination. Pawpaws, especially younger trees, do typically abort many of these fruitlets at this stage. Slightly larger fruits stand a much better chance of fully maturing though some of each cluster will still often abort later on. Probably things like the maturity, health and energy of the tree, the amount of sunlight and water determine how many fruits, if any, that the tree will sustain. Not much really to do at this point other than guard against freeze damage as we are very early in the season for this stage of development, water during periods of decreased rainfall and finally harvest before the critters beat you to it.

I know several fruits make "fake fruit" where an unfertilized flower will still swell up as if it were going to produce viable fruit, and then simply stop and reabsorb the fruit/let it fall off.

If I had to make a guess, I would say the tree may simply not be mature enough to produce fruit yet. Some trees may start fruiting in 5 years, some may take 20. Never know when one may be a late bloomer (literally).

I have one pawpaw tree, an NC1, that either because of variety or location consistently blooms a week earlier than any of the others. During typical years, (this year differed as all the early blossoms were frost damaged)the early blossoms, which I assume are not cross pollinated, will fall off without thickening of the stem or elongation of fruitlets. It is only the later blossoms that have shown these changes, that is those that had the opportunity to be exposed to pollen from other trees, Because of this observation, I believe that when I see thickening of the stem along with elongation of the fruitlets that these are the result of pollination and not "fake fruits."