The dead cow (and her basing) is fabulous. And I love the colour scheme on the figures.
Oh Chris, that's a real shame if you have to sell them on because of the size discrepancy

I think, unfortunately, whilst it's true that the Bloody Miniatures are (by design) at the large end of so-called 28s, to fit with Bicorne and Renegade, part of the issue is that even within a range, different figures have different height and stature.
The sizing of the Warlord ECW metals is a bit all over the place. Those skirmishing dragoons of theirs are weirdly skinny and slight. Whereas the Bloody dismounted troopers (cos of all the armour, helmets and gear) are the chunkiest of the lot.
If you compare other figures from the two ranges, you can see there's actually not much difference at all (below: Bloody M on the left, Warlord on the right).
You're probably OCD (like me!) when it comes to keeping a consistent basing convention across all the figures in your collection.
But if you weren't (

), then I might suggest solving the height discrepancy by sticking with slottas for the more diminutive Warlord figures, but going with penny washers or coins for the Bloody Miniatures.
Viz.

Doesn't really address the difference in overall stature, but would certainly make them look more akin on the tabletop

Cheers.
Richard