You shouldn't change the logo. You should instead be able to have a discussion with them about the effect of scaling on logos such as theirs.

I can see that it would look impressive on a van, but when it's really small, as on their web page, it looks funky, like there's a mistake in it. Just don't change it without discussing it first! Tell them you can improve the way it looks on the website while not changing it on the vans!