does sss(subsurface scattering )effect in filament affected by view direction when using the subsurface shading model?

[ilyfrd]

I found that the sss(subsurface scattering )effect in filament is affected by view direction when using the subsurface shading model, but I thought that the effect should not be affected by view direction, the subsurface color component should not change when view changes. Can someone tell me what is the truth ?

thicknessDemo3.mp4

[ilyfrd]

to put a supplement, i use ibl lighting only. I have tested that if I only use direction lighting , the sss effect looks right. but i still can't understand why the effect should be affected by view direction when using ibl lighting ?