Two varieties is not that important. Having a pollinator will produce 15-20% more fruit. Avocado flower pollen is VERY bitter. Bees prefer it the least to any other pollen. So if you have any other flowers near by, they will not pollinate your avocado!
The fix... Mix a spoon full of honey into a water sprayer (with about 1/2 gallon water) and mist as many flowers as you can reach. The typical successful pollination ratio is 1 to 1,000 fruit to flower. The worst of any fruit. This method can increase pollination exponentially.
Watch Gary's recommendations on the Laguna Hills Nursery you tube channel for more info.
(edited to add water)
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