With both Outputs connected, there’s positive flanging on the Left / Channel 1 Output, and negative flanging on the Right / Channel 2 Output. That’s a useful, unique configuration as-is. But positive flanging will reinforce those same frequencies that you want to ‘disappear’ on the negative side.
An alternative form of “intense negative” flanging – using the JET sub-TYPE – might eliminate the need for creative re-routing. [ I do notice a heavy bias toward the Left / Channel 1 Output, though. ] Any of these approaches benefit from a wide frequency spectrum to ‘chew on’: a full mix, synth bed, overdriven guitar.
If you’d like the cancellations to ‘hang’ a little longer, switch the SHAPE from TRIANGLE to SINE.
But ‘thumb on the tape reel’ flanging is never perfect. Certainly not cyclical like the TRIANGLE LFOs found in most flangers. That’s where the 2nd row modulation comes in; injecting a touch of RANDOM changes to DEPTH and SPEED. Those modulations are overlaid on the TRIANGLE sweep; breaking up its regularity.
Beyond straight-up emulations, total cancellation can be used to create doubling effects. For a more modern take on negative flanging, this preset is based on a mild ENVELOPE sweep. In turn, that is randomly modulated by very small amounts. The generated ‘2nd guitar’ will fade in & out. Turn up the INTENSITY (feedback) to erase any doubts about its flanger origins, and add some synthetic bounce & bite.