Have you tried other baskets? When using a SSP flat burr with a more unimodal particle distribution & with light roasts I generally move away from higher flow baskets such as the precision LM or VST. (Not always...some processing methods of high end coffees like Geisha's I'll try the higher flow baskets to see if it gives me what I'm after) I'd suggest trying the E&B super fine or the Espresso parts HQ (I prefer the ridged one, others prefer the non ridged, the shape is different between the two), they are marketed as 14g but easily hold 18g of light roast. That and lower your extraction pressure, add an amount of preinfusion and you have some more options to try.

I haven't tried other baskets. I have a 21g no-name basket as my other option. I need to pickup some ore baskets to experiment with. Thanks for the suggestion.