FXFX jet merging jet radius

Hello,

I was trying to see if jetradius parameter can be tuned in FXFX for better jet description. And when I change the value it gives me the message below.

^[[1mFor consistency in the FxFx merging, 'jetradius' has been set to 1.0^[[0m
^[[1;34mWARNING: You are running with FxFx merging enabled. To be able to merge
    samples of various multiplicities without double counting, you
    have to remove some events after showering 'by hand'. Please
    read http://amcatnlo.cern.ch/FxFx_merging.htm for more details. ^[[0m

So I think FXFX jet radius necessarily needs 1.0 in Pythia, so that's why MadGraph_aMCatNLO is forcing it to use 1.0. Can you confirm if my understanding is correct? In CMS, there are some reports on mismodelling of dR(jj) below 1.0 with DY FXFX samples with some strange structure-like shape so we were suspecting this was the issue + wondering if we can also tune this variable.

Regards,
Sihyun.