Yeah the rule is tucked away on page 80:
"A model should always be mounted on the base it is supplied with."
'Should', eh?
Hardly a cast-in-stone rule........
I was lucky enough to discover fantasy and gaming before GW even existed and find concepts like base sizes, WYSIWYG and (especially) having to use certain models (or certain
manufacturer's models.....) to play a
GAME somewhere between disturbing and ridiculous.
I will use the models I like - regardless of who makes them - and should any issues arise due to them not conforming to a certain companies' parameters in some fashion, a solution wil be found to make the game make sense.
Worked fine in the 70's and 80's, and guess what - It still does!
At least if you manage to think outside the profiteering and marketing box.
I can to some extent understand that GW do not want people to play with other manufacturer's minis
in a GW store or GW tourney, but why they would try to discourage people from being creative with their own product is beyond me.
Didn't use to be this way only about 10 years ago.....