If a field is set to required, it is mandatory for the prefill? Doesn't seem right.. what am I doing wrong?

I have fields in my form that I need to have filled in by Participant 1, but only if we have not filled the field already during pre-fill.  

If I set "Select Participant" to "Participant 1", it is not available for pre-fill at all.   The client HAS to fill it themselves.

If I set it to "Anyone" and check "Required" on the field, pre-fill HAVE TO fill it in.  It's mandatory before we can even send the form out for signing. 

If I set it to "Anyone" and not required, the client does not have to fill it in even if we have not either.

SO - is there a way to make a field mandatory for Particpant 1 if not already filled in by Prefill? 

I have tried work arounds such as copying the fields and trying conditions - show this if that is equal to...  etc.  or "hide if field-x equals..."   -  but hide does not really "hide" the field - it leaves a hole in the document.  IE - when hidden, it does not show what is under it - it is just a white block. 

Anyone have a workaround? 

Thanks for any help!