As far as I know, frosted surfaces smooth out tint shifts and beam artifacts. You can see the direct comparison in the famous mauka’s review on KR4. At the same time, the frosted surface diffuse light therefore are more noticeable from the very side. I think this may be the reason why you notice more light from the side. You are seeing diffused light on the frosted surface, which you wouldn’t see on clear TIR optic.
By the way, when I shine D4v2, KR4, and TS25 on a white wall, I see TS25 hot spot is more focused compared to the other two. So, I think the TIR in TS25 is more focused by design even with the small frosted spots.