Lowering Q1 exit increases sensitivity in LA ICP MS, what is the explanation?

Hi, we have an 8900 QQQ coupled with an LA. (LA-ICPMS)

I have noticed, since sensitivity had gone somewhat low through time, that manually tunning certain parameters increases sensitivity. (lowering sample depth, etc) The most critical is Q1 exit, which is automatically setted by autotune between -4 and 0 most of the times. (Aspirating solution 1 ppb of masses of interest, He mode)

But after that, we do a manual tuning with the LA using NIST 612; and lowering Q1 exit always increases drastically all counts. (The only problem is that masses 29 and 56 (air mases) become too high sometimes.)

What are the implications of lowering the Q1 exit? I have done some research but most manuals focus on "cell parameters"

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