I don't know. The larger the area of the water-air interface, the faster it will respond. But, the smaller the volume of the air gap, the faster it will respond. My guess is that it makes no practical difference if the water is up in the trumpet a few millimeters or less than one millimeter. If the water level is too high in the trumpet, the local CO2 concentration in the tank water may be slightly lower, making the drop checker read low, but that effect may be very slight.