- Edited
Few things IMHO!
- The decaf beans do not look that large to impact the issue at hand ! I have seen a lot larger beans like from El Salvador requiring a little finer grind for standard coffee.
- Coffee from, for an example, Guatemala, Costa Rica, El Salvador are relatively less soluble / difficult to extract. Your grind is perhaps enough, although you might try a tad lower, if possible. If this is not possible, you might consider a little higher dosage. In general, my dosage is 0.5/1.0g lower for decaf.
-Certain decaf requires a longer resting time even 3 to 4 weeks.
How old are those decaf beans please ?
Thx