When I go the Art’s it shows...
Shimano 10 speed Road cable pull = 2.3mm
Shimano 11 speed Road cable pull = 2.7mm

10 speed cassettes are spaced at 3.95mm ctc.
11 speed cassettes are spaced at 3.74mm ctc.

I think it is just math.
10 speed road RD actuation - 3.95/2.3 = 1.7
11 speed road RD actuation - 3.74/2.7 = 1.4

Tiagra 4700 shifter cannot pull the same as 11 speed cable pull because you can use an 11 speed RD and move it 3.95mm.

Tiagra 4700 pull - 3.95/1.4 (RD actuation) = 2.8mm cable pull.

If it is correct that any Shimano 11 speed road RD works with Tiagra 4700 shifters, then 11 speed GRX RD should work with Tiagra 4700 shifters and a 10 speed cassette.

John