How have you found playing in 28m - did you make any special amendments?
Have you rebased your 28's in groups or used them singly?
I've played quite a few games with 20mm figs abut now I am planning some games based around Norway and France 1940 using 28's
I was planning an article about this, as it has been my concern for a long time. I'll make it short: this is method one:
Your minis must be mounted on washes / 5 eurocents coins / some other magnetic-reactive stuff. Mine are 2.5mm round washes (0.05 euro each)

Then pick any base you want and glue 2-2.5 mm magnets (mine are 60mm Litko bases and Drachenhole magnets) - I don't have the painted+flocked ones here along, but believe me, they look better.

That's it, they stick perfectly. If you prefer more facing precision, Litko makes good square too. Otherwise Litko also has 60mm square bases with holes for slottas (PM me for that). Make sure everybody uses the same size and it's done... CF has got no measures, so no adapting is necessary!

And, by the way... they really cling

.
P.S.
I didn't just base them on the 60mm because I like playing skirmish too (NUTS!, DH/C7B), so I can use the minis for both.
Hope that helped.