@mijostyn, what were the dimensions of your OB/Dipole sub frames? Were they H-frames, or W-frames? Linkwitz chose to go with the W, Danny Richie with the H (though he provides plans for both on his GR Research website).
Did you incorporate the mandatory shelving circuit (6dB/octave boost below 100Hz) to compensate for the endemic dipole cancellation? The OB/Dipole version of the Rythmik plate amp does, and the sub absolutely reproduces the bottom octave. Honest! ;-)
Siegfried Linkwitz was nothing if not a methodical scientist, measuring everything. He published all the test results of his measurements on the LX521 loudspeaker, including those of its’ OB/Dipole woofer. That woofer too reproduces the bottom octave, and the LX521's electronics include the OB/Dipole-mandated shelving circuit. That shelving circuit is NOT optional in an OB/Dipole sub, it is mandatory.