I have an ecm angled, bottomless portafilter that came with a triple basket. The triple is so big it seems that even with 20g in it I have too much head space and end up with a soggy puck.

How does one pull these bad boys?

try 24g and grind a bit more coarse

Soggy puck isn't fatal, in fact it means little, how's it taste?

24g in a 21g basket?

May as well pack 20g into my 18g basket then, no?

Taste is okay. Not as easily consistent as with my standard 18g double basket pulls.

yeah you can pack in a weight range usually, depends on roast level and grinder setting and machine's headroom

I have 22 and 25g VST baskets. The 22 is my standard, the 25 I use for Americanos.

No big deal. To get dry pucks, overdose by about 1g with medium roasts, more with light roasts. The important things is to get the coffee to just about fill the head space. The coin test can tell you that pretty quick. For all my Viennese roasts, I use 23g in the 22g basket. Light roasts can take 24g or even more.

Adjust grind and timings to taste. Even and consistent tamping is critical because there is a lot of compressible material in the puck. Therefore, variations in tamping pressure and angled tamps have more effect than they do with thinner pucks (my theory). There is more opportunity for tamping errors to cause large changes in resistance from place to place on a given puck, and from puck to puck. Varying resistance will have your timings wandering all over the place. You learn.