Best practice is to use Traditional Full-Volume BIAB. We consider this to be a Continuous Sparge, Continuous full grain contact with 100% of the water going into the boil. And mash (/Continuous Sparge - combined process) for a full 90 minutes, then a 90 minute Boil. Don't cut down your mash time or your efficiency will likely suffer.

When we hear of efficiency problems with BIAB, it normally happens when people try to get "cute" with the process... Examples include less than full volume mash with sparging, less contact time in the mash, etc. If your pot is too small and you are making a larger batch, it is possible to withhold water, do a sparge / dunk sparge / etc. to try and make up some of the lost efficiency. I've done this when making extra large batches. But it's lots more work. Best practice is the traditional, full volume BIAB process!

Best of luck to you, and let us know if more questions.   

BufferNuggets, See Section W of the BIABacus for where to input "water used in a sparge" if you choose to go that way.  If your target VIF and gravity give the red warning about mash volume approaching or exceeding the kettle volume, it is either time to get a bigger kettle, make a smaller batch or use Section W. It will reduce your mash volume as the sparge is poured over the hot wet grain bag after it has been pulled from the kettle. You have to have a plan for how to do that. I tried using Section W with 2 to 3 liters for increased batch size / increased efficiency on a 5.5 gallon (20.8 L) VIF scale and found that I got about one more 12 oz (355 mL) bottle compared to maxing out the kettle and not using Section W. It was not too much more work with my side-by-side gas burners, but I rarely consider doing it now. Your choice.