Question about tyre vs rim width

I’ve recently fitted a pair of 25c Veloflex Masters to a fairly wide set of rims, 21mm internal and a huge 32mm external (Cannondale Hollowgram 45s if you’re interested). Having fitted them, I can clearly see the tyre is at least 3-4mm narrower than the rim itself. Is this an issue? I’ve heard off the cuff comments about rims striking the ground under load or tyres failing due to more shoulder stress, is that truth or chat? Cannondale recommend 25c/26c tyres for maximum efficiency but it looks so odd!