I feel like there was some improvement with this interaction in AC25, but I do not recall, nor am I using it... Anyway, I do not usually model like this. These thicker sections of slabs are usually structural beams or footings, so I do them as separate Beams on their own layers.
AC22-23 AUS 7000 Self-taught, bend it till it breaks. Win10 | R5 2600 | 16GB | GTX1660