Passive radiator with closed enclosure’s characteristic

I have an opportunity to listen to a closed enclosure bass-loading system with Qtc of 0.5. And, I do badly like it. I wish to build my four-way floor-standing loudspeakers project with this specification. My project is originally planned to be passive radiator system where the passive drivers are already arrived in the stock. Yet, the cabinets haven’t been designed and constructed. Thus, I’m curious to know whether it is possible to create a passive radiator system whose response or alignment resembles that of the closed enclosure with Q of 0.5 system. Has anyone ever tried it? If so, could you please instruct, or better provide the procedure, how to achieve it?
 
Tune them low
Can I do that by this method?

First, treat it as a traditional closed box, calculate box volume for the active driver with the lowest Q (Q = 0.5). Then, double the box volume when installing the passive driver.

For instance, the calculation suggests closed box volume for the active driver alone is about 2.0 cu.ft. When installed with the passive driver, the whole box volume should be increased to 4.0 cu.ft.
 
Loudspeakers wirh ports and such with passiver radiators are both bass reflex, only with different kinds of resonators. There is a difference in the steepnes of the lower filter slope: that of BR-boxes with PMs tends to be steeper, so also the group delay there is a little bit higher.

Kind regards
Michael