As a new home espresso enthusiast I would really appreciate learning how to best vary a dose for a typical double or my triple in the bottomless portafilter.

I fully appreciate how to add to the dose by packing tighter before tamping so the grounds are not as fluffy but what about using less coffee? I am under the assumption that every dose needs to start at least level with the top of the basket or more usually above it such that you can distribute evenly before tamping. This would seem to be necessary to get a puck where the extraction is uniform. Is this assumption true for good/sound technique? If so then can I assume that the lowest doses for a given basket should include enough grounds to top it off? I have not (yet) bothered to weigh my coffee.

I appreciate the knowledge base here and it has already helped my learning curve.

If you vary the dose regularly, you will need to weigh, since consistent dosing without weighing requires a very set, very stereotyped ritual.

On an LM, Cimbali, or Faema style double basket, leveling and swiping will dose around 16.5 to 18.5 grams depending on grinder and coffee. To dose less, the simplest system is to swipe the basket with an icing knife or other piece of plastic with a curve cut in. This will scoop below the level of the basket.

One can also dose by time. ±5% repeatability is possible with a 0.1s timer.

I can add to what Jim said base on my own experience. Some machines are very sensitive to dosing accuracy while others not so much. Since you did not specify what equipment you are using it is difficult to give specific answers.

I have a Quickmill Anita with a Compak K3 touch grinder.

I've dialed in/calibrated the touch feature so that two hits of the touch bar doses enough to fill my double basket such that after distributing with my finger to four sides I usually push off and waste a small amoount (< 1 gm estimate) of grinds. I tamp and pull. I'm now trying to just vary grinder setting and temperature to get ideal shots. This seems to be working beter and better as my technique improves and I get feedback from the machine and my taste. At some point I will weigh my dose on a digital scale but I'm going by how the shot comes out and taste right now.

My question about dosing and the top of the basket was really for my knowledge base and to get ideas about what is possible and how to improve my espresso. I'd especially like it for my triple basket as that is where I see people using the most variable doses of grinds.

Thanks for everyones help

Well I've done some homework and for those interested I found some interesting answers here

controlling-shot-extraction-pattern-t583.html