I say, if it feels right for you, then do it that way. You may be lucky and trained, so that your systems works well on fast-sauna pairing.
I believe the negative experience of ppl with sauna during fast is when the body is in mineral imbalance, or the skin looses for some reason too much good electrolytes together with the toxins, then sauna makes things worst by making you loose even more minerals.
There is a school of dry fasting, Ukrainian: https://www.youtube.com/watch?v=lQkPrLnp0BM
Please, continue sharing.
DL