I'm afraid I don't have a scale shot myself, but I can give you my experience on this very subject.
I bought both the French and English HYW kits to kitbash with my large WOTR collection.
They are indeed at a bigger scale. There are several other things different about them. This is what I found...
1 - They are taller. It's very clear when you put them side by side. Of course not everyone is the same height, and mixing some of the taller HYW models into a WOTR unit should look fine. The height difference is less noticeable, if at all, on some of the French bodies which are in leaning forward poses. On others, it is more obvious.
2 - They are both rather different in sculpting style. I believe Michael Perry did the WOTR ones, and Alan Perry the HYW ones (may be wrong though). The HYW have finer detail to my eye, and are probably technically better sculpts.
3 - The HYW may be technically better, but I find are less useful for kitbashing. The 5 WOTR boxes are brilliant for mixing parts and such... The HYW sets, in my experience, are just great as they are 'off the shelf'.
4 - The two ranges have different head joins. The WOTR use a ball-and-socket, the HYW ones have a flat join. Also, most of the HYW ones have hoods or mail coifs. There are ways around it, but mixing heads from the two sets isn't always that easy (there area some combos which work easily though). Also, the knights from both the English and French HYW sets come with the heads already on the bodies (and can't be cut off without messing up the mail aventails).
5 - Arms from both sets switch across VERY easily. I have found the WOTR shouldered pike arms (converted to halberds and bills) look great on the HYW french bodies. And I have used loads of the HYW arms on my WOTR bodies. For the two-handed weapon arms, you may need to do some minor cutting and filling to make them fit perfectly flush, but nothing too tricky.
6 - The longbows from both sets are noticeably different in size. If you are used to the WOTR ones, you will find the HYW english longbows MUCH longer. I've actually used some of the HYW longbow arms, but with bow hands cut off and replaced by the WOTR bow hands, to give me both some new variety in arms yet keeping the bow lengths consistent.
So, yes the scale is slightly different, and it may well be a bit of a problem if you are finicky about that sort of thing like I am. If you are thinking of getting some of the HYW boxes to spice up your WOTR builds, you may at first find there won't be as many things you can do as you first thought. However it's well worth buying a sprue or two (ebay is your friend) of both the french and english infantry sets, and both french and english knights, to get a number of bits and pieces.... Spear arms, 2-handed axes, other armoured knight arms, alternative crossbows and quivers, swords, bucklers, some heads, a few bodies that will work....