I had met a woman working at my local mall’s antique store. When I asked about fountain pens she said that while there weren’t any in the store at the moment she had one gathering dust in her cabinet drawer and that she would bring it the next day. I had thought she was bring it to sell to me but she just gave it to me for free. It was a very pleasant surprise and the pen wound up being a TWSBI Vac700! There was also a store closing sale going on elsewhere and I have quite a few Christmas/Birthday presents. Today was a very lucky day.
From my experience vacuum fills are the only type where you can achieve a full fill without flipping the pen upside down while filling with a Travelers inkwell like this https://goldspot.com/products/pineider-pen-filler-portable-inkwell A full fill seems to help with flow reliability, or at least it does for my vanishing point.