I don't think it's possible, or even desirable, to have all the fingers at 90 degrees to the fingerboard. I used to think so, but in Pumping Nylon
Scott Tennant shows very clearly that the most natural positions for the fingers are like this:
1. The first finger plays on the left side of its tip.
2. The second finger plays just to the left of its tip.
3. The third finger plays just to the right of its tip.
4. The fourth finger makes contact on the right side of its tip.
Scott plays LOTS better than I do, so he must be right.
When you play that G7 chord with the C# (it sounds ugly...), which string buzzes? The F on the 1st string? The open B string being touched by the 1st finger? Other?