Silence: Always vs While phone is locked ?

I am missing calls most of the times on my iPhone (5s). Although I ensured that the ''Do not disturb'' button was off, this still happen way to often and I've not been able to pinpoint the cause.

However, on the ''Do not disturb page'' I see something which I have a hard time to interpret and which seems to me a little contradicting:

SILENCE:

Always: if you select this option, it says: ''incoming calls and notifications will be silenced while iPhone is either locked or unlocked''

While iPhone is locked: ''Incoming calls and notifications will be silenced while iPhone is locked''

Seems that you need to have one of these 2 options ''ON'' and there is no way to put both ''off''... However, following that logic, it's like, if you choose first, you'll never hear you phone ringing... And if you chose the second, ''good luck'' if someone calls while your iPhone is unlocked (which likely will happen within the 30 seconds or the 5 minutes *it is* unlocked !!.... )

Am I missing something ?... I had several people read the same, and we all wonder how to read it...

Rob