I will give you an educated guess:

I did some test shots with the R5 in full frame mode with image cropping in post and compared them to the taking shots in the 1.6 crop mode .... there was very little difference in image quality.

I suspect if you shoot RAW you could easily crop a 70 mm shot in post processing to simulate 105 mm with no problem or simply shoot in 1.6 crop mode which gets a field of view equivalent to 112 mm on a 70 mm lens.

In crop mode you get less megapixels (17 if I remember correctly) but the resolution is still quite reasonable.