I always used nipples with the whistle cut - as supplied from Moroso - and installed them with the end cut parallel to exhaust flow - i.e. turned 180 degrees from your illustration - and deep enough to get the whistle cut well into the flow.

Never checked vacuum but they worked well I thought. Could free rev the engine and feel the pull on the hose. Cleaned up the moisture in the valve covers after the engine warmed up. Had to keep an eye on the check valves. They would fail fairly regularly and need to be replaced.

The addition of mufflers - even just the collector style - substantially reduced the effectiveness of the system.