Windows 7 x64, ProgDVB Pro x32 6.80.1, DVB-T

Hi, when watching SD channels everything is OK, but when there is a channel in HD, i can´t see whole the screen - I must use zoom function to reduce to 75%. If i do it, after switching to SD channel i must reuse the zoom from 75% to 100%.
What can i do for watching channels without troubles?
I tried everything in Video settings with ratio, blackbars, autodetect real video size, but nothing helps.

Thank you for reply.

It is zoom or letterbox for every channel independently.

Yes, but current channel broadcasts some program in SD, another in HD.
Location: Czech Republic
norm: DVB-T
Channels CT1, CT2, Nova, Prima....all of them broadcasts 70% of time in SD, 30% of time in HD. I must always switch to another zoom level which is confusing. Any solution on this? Thank you much.

Settings->Options>Video->geometrial->Auto-detect video size ?

As i mentioned in my original question, this does not help.
It seems to me checking this function has no influence on the screenplay. Simply nothing differs from unchecked. Nobody else has similar problem like me? Nobody will help me?