Run 1816 is an HRS-R run triggering on modified T6 (S2m-R + GC-R -- the makeshift positron trigger), with the sieve only partially inserted. I see no hint of contrast as you look across the acceptance (I'm just using the tg_th and tg_ph variables in the standard online analyzer.
But there must be contrast: the scaler rate for the modified T6 (S2m-R + GC-R) goes DOWN by about a factor of 2 when we remove the sieve. [Why the sieve INCREASES the positron rate rather than decreasing it is another puzzle.]
It may be that the "partially in" position was almost entirely in (note the T6 scaler rates were very similar for 1816 as for the sieve-in runs), so this wasn't a good contrast test.