So far I have only used PLA to support PETG and vice versa (because it is dirt cheap and works) and I have experienced weakness in the printed model at heights where support interface was used.
IMO it is caused by support material contaminating and weaken the bonding of the print material. You need to flush a lot more volume of print material. Last time I tried I think about 3 times the default volume was OK. I think the calculated flushing volumes are just based on color relative contamination so not really relevant.
As for other settings using support interface I set Z top and Z bottom to 0, top and bottom interface layers to 1, top and bottom interface spacing to 0, and interface pattern to concentric (I use the softfever fork, the stock version might not have all those settings). Apart from less interface layers I don’t think they will make a difference to the model strength problem. They just give the best finish on the supported surfaces and minimize material swaps.