For comparison the TF Corsair tires are 4.5in dia. And it has a 1in. longer wingspan than the H9. The Robart 5in aluminum wheels set for the P-51 are actually very close to 5in so it’s strange the set you bought are that far off.
Take a look at Sierra Giant Scale for wheels if you want something better than Robart.

I dont one like the look but I’m kind of interested in the inflatable Dubro 4.5in wheels because you can run them at low pressure. The same wheels in solid foam are pretty stiff. It would be cool to take the gray plastic ugly wheel out and replace it with an aluminum one so you have the best combination.