The other option is to grind very fine and tamp hard leaving perhaps 5mm of headroom for the fine coffee to expand into. I have tried this and it does work- but it seems harder to mail the correct grind than going coarser and filling the basket. Having a naked portafilter does help to see what happens during pre-infusion- looking at the bottom of the basket you can see how well the puck holds together and how easily or hard it is for the water to flow through it.

It seems like I need about 15g of coffee to get that kind of head space (to get around 5mm of head space with some taps and a light tamp). Is that too much for a double (double pull)?

15g is right on for a two-pull shot. I often go 16g. But each coffee has a different weight:volume ratio. Some 15g doses will top it out, other coffees can take 16g or more. Depends also on the grind and tamp.

Since I've been using the bottomless PF I find it takes a little fine-tuning of the grind to get a perfect cone extraction. Small variations in dose or grind can lead to extractions that don't look perfect. But they taste great anyway, so I'l let taste be your guide.

In simple terms, if find it easiest to dose consistently full, then adjust the grind to get perfect flow. For my tastes, perfect flow means: 1) One 10 sec preinfusion with the lever down, followed by a slow 1/2 rise of the lever 2) when one drop of coffee falls, a second pull down, wait 3 secs, then another 1/2 pull - some coffee will flow slowly, 3) a third pull down, 3 sec wait, then the full pull. The coffee pours in a perfect cone from the basket.

VERY similar to my technique Jack. What I've been doing lately for milk based drinks is doing a second full pull, but resisting the lever on it's rise to prevent the typical second-pull gusher. Works very well, and the resulting higher-volume total pull is quite tasty.

Bottom line is the more I use, and learn about, this machine, the more impressed I am.

This last weekend I was in Brooklyn so I visited Cafe Grumpy a couple of times, Blue Bottle and a couple of other places. I was interested in how Grumpy pulled its own heartbreaker blend because I started out with it and suffered humiliating defeat. Well the heartbreaker at the cafe tasted great. None of the overly strong and unpleasant flavors that I was getting at home. I still had a couple of pounds frozen at home and I knew I had my work cut out for me. I haven't pulled anything even close with the heartbreaker or the redbird or the terrior blends that I have tried (about 12#'s). Sigh.
So I get home, pull some Heartbreaker out of the freezer and pull two shots back to back that tasted as I remembered from the cafe. I am more than a little pleased.

Now if only I could get that thick steamed milk that the cafes were able to produce. Any tips with the Export? I have have a 12oz espro troid pitcher that I keep in the freezer (seems to help), I steam cold whole milk to about 150f (65.5c).

I had two double filter baskets and one seemed to let air/water go through at different rates. Not while pulling a shot (still too many variables in my technique to be sure of that), but while running water through the baskets or blowing through them. So I bought two more (it makes pulling 4 in a row easier) and they both have similar characteristics to each other but less flow/more flow than the two I already have. Does this kind of thing make a difference? I will mark the baskets and try to see if I can tell. I was surprised by the differences between them.

I never noticed any difference between baskets, but I never really looked. Can you see visible differences if you hold them up to the light?

Steaming milk does take a little practice. Try to keep the tip submerged so only the smallest amount of air enters. If you can hear it very much it will be too much air, and foamy. If you keep it submerged a little further, and try to get it swirling in the pitcher, you be making "latex paint" consistency milk in no time. Using a little more milk in the pitcher seems to help too.