Dear Wim,
I have checked the apertures that we have in the transfer line files in the elements
DIS : square aperture 50 mm hriz, 100 mm vertical .
DVT : bore diametre 140 mm
SMV : square aperture 68 mm (horiz) 30 mm vertical
BVT : bore diameter 140 mm
In the DIS and SMV the ratio between the aperture and rms beam size is around 5 for both planes. This is as low as we feel confortable to go, so these apertures shouldn't be reduced further.
In the DVT and BVT, we have some margin, so if you want to reduce the aperture by some 20 % we can discuss.
Let me know, alessandra