Don't get too hung up on hight of figures,people are dramatically different heights,
I've spent alot of time answering people who send photos of vehicles and try to size a vehicle by the people in the photo.
You need to deciede what height a 28mm figure is to you,as a rule of thumb take it as 5mm to a foot.the only constant is the size of the weapons and equipment.if they fit well then it should work well. Throw in the odd head swap and they'll tie in nicely.I use copplestone,and great war,with my own and my vehicles I personally prefer to mix and match sculptors and manufacturers it gives a more human feel to my units.hope this is helpful.